The Pumpkin
a library of selected
writings of
Douglas A. Kerr
you are at
the
Index page
The name of this site, "The Pumpkin", alludes to the hollowed-out pumpkin that figured in the infamous Whittaker Chambers/Alger Hiss espionage case in the late 1940's as a storage spot for "special" documents. I hope these documents are equally (although of course differently) "special".
The current areas are as listed below; click on a topic area to jump to that section of the index.
At the listing for a particular article, the title is a hot link. Click on it to download and view the article.
Table of Contents
Optics, photography, and imaging
Music and electronic music, film, and video
Mathematics, science, and engineering
Transportation and Agriculture
Information systems and computers
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Optics, photography, and imaging
Adding Vertical Tilt Positions to the Canon Speedlite 550EX Flash unit
Annotation Metadata in Digital Image Files
APEX - The Additive System of Photographic Exposure
Oblique Astigmatism in Camera Lenses—Meriodional and Sagittal MTF Response [Title changed] Updated
Autofocus Accuracy Specifications in Canon EOS Digital SLR Cameras
Average Scene Reflectance in Photographic Exposure Metering
The Canon sRaw and mRaw Output formats
Canon EOS 20D and other similar cameras - Behavior of Custom Function 4
Canon EOS 20D—Replacement of the Shutter Release Switch
Characterizing the Output of Photographic Flash Units
Chromaticity and Chrominance in Color Definition
Chrominance Subsampling in Digital Images
THE CINE-KODAK LINE OF MOTION PICTURE CAMERAS
The film and cameras that made “home movies” possible Renamed as "The Kodak Ciné‑Kodak line of motion picture cameras".
The Kodak Ciné‑Kodak line of motion picture cameras Cine-Kodak Royal Magazine added (with picture of Princess Elizabeth using one).
The Kodak Ciné-Kodak Special 16 mm motion picture cameras
The Kodak type S lens mount and the Ciné-Kodak Special
The film transport mechanisms of Ciné-Kodak movie cameras
Lens mounts of Kodak Ciné-Kodak movie cameras
Colorimetric Characterization of Digital Camera Sensors
The CIE XYZ and xyY Color Spaces
The CMOS APS Digital Camera Sensor
Depth of Field Calculator - Excel spreadsheet
Depth of Field in Film and Digital Cameras
Derivation of the "Cosine Fourth" Law for Falloff of Illuminance Across a Camera Image
Describing Digital Camera Sensor Sizes
Describing the Potency of Light
Determining MTF with a Slant Edge Target
Digital Camera Sensor Colorimetry
The Effect of Inserting a Flat Glass Plate into the Optical Path Downstream from a Lens
Exposure Control in the Canon Wireless Flash System
Exposure Metering Modes in the Canon EOS-300D (Digital Rebel) Digital Camera
Format Size in Digital Photography
The Fourier Analysis Tool in Microsoft Excel
A Gaffe in the ISO Standard for Photographic Exposure Meters
The Hemispherical Receptor Incident Light Exposure Meter
The HSV and HSL Color Models and the Infamous Hexcones
The ISO Definition of the Dynamic Range of a Digital Still Camera
Improved Beamwidth Control in Canon Speedlite Flash Units
JPEG Compression of Still Images
The Kodak type S lens mount and the Ciné-Kodak Special
The La Crosse BC-900 Battery Charger/Tester/Conditioner
Lens Principal and Nodal Points
M, X, and V on Camera Shutters
The Mathematics of Extension Tubes in Photography
The mechanics of the JPEG image encoding system
Describing the speed of Morse code transmission
Metameric Error in Digital Photography
A Metric for Chromaticity Difference
Mosaic Sensor Arrays in Digital Photography
New Measures of the Sensitivity of a Digital Camera
Norwood’s dome: a revolution in incident‑light photographic exposure metering
Oblique Astigmatism in Camera Lenses—Meriodional and Sagittal MTF Response
On the Term “Field of View Crop Factor”
Parallax
Suppression in a Target Rifle Aperture Sight
The next article is a companion
to this one
Parallax Suppression with a Target Rifle Aperture Sight—An Optical Demonstration
The paraxial approximation in optical system analysis
Pixel Resolution in Digital Photography
Photographic Exposure Metering and the Infamous “18% Calibration”
PHOTOGRAPHIC EXPOSURE METER FAMILIES
The GE "DW" line of photographic exposure meters
The "Norwood Director" family of photographic exposure meters
The Weston Master family of photographic exposure meters
Polarization of Light and Polarizers
Programmed Automatic Exposure in Canon EOS Digital Cameras
The Proper Pivot Point for Panoramic Photography
Quantizing and Noise in Digital Photography
Replacing the Focusing Screen on the Canon EOS 20D Digital SLR Camera
Sampling, Aliasing, and the Blur Filter
Setting Camera Exposure in Terms of Ev
The Secret Life of Photographic Exposure Metering
Shift of the Plane of Best Focus With Shift In Film Position
Some Principles of Photographic Optics
The Unsharp Mask Process in Photographic Image Processing
The Canon USM (Ultrasonic Motor) Autofocus Drive System Just now indexed here!
Vision Correction in Camera Viewfinders
White Balance Color Correction in Digital Photography
White Balance Diffusers in Digital Photography
Optometrics
Evolution of the optometric refractor—the DeZeng-American Optical‑Reichert dynasty
The Focimeter—Measuring Eyeglass Lenses
The “mustache” of the American Optical M603 Lensometer
Plus and minus cylinder notation in ophthalmology and optometry
Principles of Eyeglass Prescriptions
The Refractor/Phoropter—An Important Tool in Vision Correction
Tillyer’s Additive Trial Lens System
Trial Lenses in Vision Correction
The Vertex Power of Ophthalmic Lenses
Music and electronic music, film, and video
MIDI - The Musical Instrument Digital Interface
The SMPTE 27.97 fps drop-frame video time code system
Dallas Telephone numbers 1915‑1961 NEW, revised
The detached contact system for telephone switching circuit schematic drawings NEW
The first North American mobile telephone system
The hybrid coil circuit in telephone transmission systems Editorially revised
Manual Telephone Switching Substantially revised
Message registers in telephone switching systems NEW
Multi-party telephone lines–note
Multi-party telephone lines Substantially revised
Ringing in multi-party telephone lines Substantially revised
The origin of the 1.42 unit stop element in the North American 5‑bit teletypewriter system
Operation of traditional coin telephones
THE PANEL DIAL TELEPHONE SWITCHING SYSTEM
The panel dial telephone switching system
The Panel Dial Telephone Switching System—Interoperation with Manual Switching Systems
The Panel Dial Telephone Switching System—Tandem Switching
Rotary telephone dials—two families—their looks and sounds RECENTLY NEW, this issue revised editorially and expanded
THE STEP BY STEP TELEPHONE SWITCHING SYSTEM
Reverting calls Extensively revised and expanded
The Teletype Corporation receiving transmitter distributor
THE WIRELESS INSTALLATION ON R.M.S. TITANIC
The wireless installation of R.M.S. Titanic
The wireless key of R.M.S. Titanic
Why was the Western Electric 500D telephone set called that? Revised with corrections
The Varley loop and Murray loop tests for fault location in telephone circuits
Mathematics, science, and engineering
Dimensional Analysis—A Tool for Guiding Mathematical Calculations
The role of “generator inertia” in the electric power generating system New
The maximum power transfer theorem Recently new; this issue updated
Power and exponential functions New
SOLAR (PV) ELECTRICAL ENERGY SYSTEMS
Solar energy—quantities, and units
Calculating the position of the sun
Principles of residential solar electrical energy systems Revised
Solar PV panels–power output ratings
Solar energy systems—solar panel and inverter power ratings Revised
What property does “magnetic field” denote? Revised, one error corrected
The Vernier scale in measuring instruments
The calibration constants of an electromechanical watthour meter New
Principles of electromechanical watthour meters Recently new, this issue expanded
Hall effect devices in electronic watthour meters New
Insulin Pens and Their Mechanisms
The FreeStyle Libre 14‑Day continuous glucose monitor system
The SkyAngel 911FD 4G personal alarm system
Transportation and Agriculture
The Oliver No. 23-B Reversible Sulky Plow
Principles of Steam Locomotive Valve Systems
Spring Equalization for Steam Locomotives
Rail Signal Aspects and Indications
The Episcopal Civil War in the Episcopal Diocese of Fort Worth
The Geometry of “Toward Mecca”
Art and craft
A Modern Automated Machine Quilting System
Stitch Formation in Rotary Hook Sewing Machines
Information systems and computers
ASCII and "ANSI" Character Sets
ASCII, Unicode, and In Between
Microsoft Excel: Number representation, precision, and accuracy Recently new, extensively revised in this issue
Image Annotation Objects in Picture Publisher 10
The names “octatherp” and “octotherp”for the symbol “#”
Scientific Notation and Floating Point Representation
Watches and clocks
Doug and Carla - an Urban Legend
Windows users: Click on the title to view the article, or right-click and make the appropriate selection to download the article.
Mac users: Beats me.
Note that the sizes of the PDF files are given in kilobytes (kB). In accordance with the recognized overall conventions of science and engineering, a kilobyte (kB) is defined as 1000 bytes. We are aware of the widely used, but unfortunate, convention in which a kilobyte (kB) is defined as 1024 bytes. This practice is deprecated by the general standards for scientific units.
There is an internationally recognized system of distinct "binary-based" multiple prefixes for units, under which a quantity of 1024 bytes is unambiguously designated a kibibyte (KiB). However, we find no justification for stating the sizes of files here in that unit.
This article gives more information on this matter.
Optics, photography, and imaging
Adding Vertical Tilt Positions to the Canon Speedlite 550EX Flash unit
The Canon Speedlite 550EX flash unit provides vertical head tilt for bounce flash operation. Detented positions are only provided for angles of -7°, 0°, 60°, 75°, and 90°. Other tilt angles are useful for various work. This article describes the modification of the 550EX to add further positions to the detent.
Issue 1, 2004.10.04. 5 pages, 1270 words, 5 photographs, PDF format, 184 kB
Annotation Metadata in Digital Image Files
Many digital image files accommodate metadata items we may describe as annotation, human-oriented information about the image or its circumstances. In this article we describe three classes of such annotation data items. We also discuss the way several image-manipulation software packages allow us to view, add, or change annotation data.
Issue 1, 2004.05.22. 16 pages, 3300 words. PDF format, 122 kB
APEX - The Additive System of Photographic Exposure
The Additive System of Photographic Exposure (APEX) provides for stating several factors involved in photographic exposure in logarithmic form. In this way, calculation of the “proper exposure” for a given situation may be done manually using only addition. Although the importance of that has largely faded since the time the system was developed, the scheme is still widely used in technical work relating to photographic exposure, especially the quantity “exposure value” (EV). This article explains the APEX system, and gives cautions about irregularities in its usage that are often encountered.
Issue 9, 2022.10.08. 21 pages, 5853 words, one appendix. PDF format, 119 kB
Autofocus Accuracy Specifications in Canon EOS Digital SLR Cameras
Canon, Inc. typically expresses the accuracy tolerance of the autofocus system in their EOS digital SLR cameras as a fraction of the depth of focus. Of interest in relating this specification to its impact on actual photographic work is how this relates to depth of field. In this article, we describe that relationship, as well as the basic significance of the specification, and of depth of focus itself.
Issue 1, 2005.06.06. 9 pages, 2900 words. PDF format, 114 kB
Average Scene Reflectance in Photographic Exposure Metering
The quantity “assumed average scene reflectance” is widely mentioned in connection with the calibration of “reflected light” photographic meters. Understanding of its significance is elusive. In this paper, we examine the actual significance of this quantity and how it plays a role in deciding upon a calibration constant for a reflected light exposure meter. We also examine the significance of various oft-mentioned values of assumed average scene reflectance, such as 18% and 12.5%, and finally discuss the use of a gray card of known reflectance to perform “incident light” metering using a reflected light meter.
Issue 1, 2005.01.30. 19 pages, 6200 words. PDF format, 159 kB
The Canon sRaw and mRaw Output Formats
Many digital cameras (including many Canon models) offer an optional form of output file in which the data does not directly represent a “finished” image but rather is a more-or-less verbatim transcript of the digitized output of the collection of individual sensor photodetectors. This is referred to as the “raw” output. Recent middle- and upper‑tier Canon dSLR cameras offer two alternatives to this output file type, described as the “sRaw” (“small raw”) and “mRaw” (“medium raw”) output files.
In this article I first give extensive background on various underlying topics. I next discuss the principles of the sensor arrangement that leads to the use of the raw output concept. Then I briefly review the “regular” raw output, what we do with it, and the advantages of operating in that mode. Next I describe the concept of the sRaw format, its important technical details, and why it is said to be beneficial. Finally, I introduce the mRaw format, and compare it with sRaw.
Issue 3, 2014.11.17. 14 pages, 4275 words. PDF format, 88.53 kB
Canon EOS 20D and other similar cameras - Behavior of Custom Function 4
The Canon EOS 20D, 30D, 5D, and certain 1-series cameras have a Custom Function (Custom Function 4, "C.Fn-04" or "CF04") that allows customization of the effects of half press of the shutter release button and press of the "*" button on the execution of automatic exposure (AE) and automatic focus (AF) functions. Four settings are available. The entire scheme is complex, with the implications varying with the combination of metering, autofocus, and drive modes in effect. This document features a chart that shows the implications of the four settings for those various combinations. The chart itself is accompanied by a narrative synopsis of the implications of the four settings and a brief discussion of where and how each might be useful.
Issue 4, 2007.11.26. 4 pages, 971 words. Chart, synopsis, notes. PDF format, 104 kB
Canon EOS 20D—Replacement of the Shutter Release Switch
The shutter release switch on the Canon 20D digital SLR camera can fail completely or misbehave. In this article, we describe how to replace the switch. The required disassembly procedure is described in detail, with illustrations.
Issue 3, 2016.11.21. 12 pages, 2860 words, 12 illustrations. PDF format, 431 kB
Characterizing the Output of Photographic Flash Units
We are often interested in quantifying the maximum “output” of a photographic flash unit. We often see descriptions in terms of guide number, beam candlepower seconds (BCPS), candela-seconds, and watt-seconds (or joules). In this article we explain the different properties we may wish to describe and the various metrics and units that apply to them.
Issue 7, 2013.10.19. 10 pages, 2445 words. PDF format, 91 kB
Chromaticity and Chrominance in Color Definition
In connection with the definition of color in such fields as computer graphics, television systems, and digital still photography, we encounter the two similar-looking, and often-confused, terms chromaticity and chrominance. In this article we illuminate the distinction between these terms.
Issue 4, 2010.10.03. 5 pages, 1390 words. PDF format, 65 kB
Chrominance Subsampling in Digital Images
The JPEG and TIFF digital still image formats, along with various digital video formats, have provision for recording the chrominance information (which conveys in a special way what the lay person would describe as the “color” of the pixels) in a resolution lower than that of the image being encoded. This concept, followed for over half a century in television broadcasting, takes advantage of the properties of the human perceptual system to reduce the amount of data required to convey an acceptable full-color image of certain pixel dimensions. There are various standard “patterns” for performing this “chrominance subsampling”, and a curious and confusing notation for indicating them. In this article we discuss the concept of chrominance subsampling and describe various systems of notation used in this area.
Issue 3, 2012.01.19. 11 pages, 3300 words, 4 illustrations. PDF format, 119 kB
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THE CINE-KODAK LINE OF MOTION PICTURE CAMERAS
In 1923, Eastman Kodak Company revolutionized the motion picture art by its introduction of 16 mm film and the first of a family of cameras to use it. The four following articles cover this development, and the "dynasty" of motion picture cameras that ensued, from four separate perspectives.
The Kodak Ciné‑Kodak line of motion picture cameras Cine-Kodak Royal Magazine added (with picture of Princess Elizabeth using one).
In 1923, Eastman Kodak Company introduced 16 mm motion picture film and a camera, the Ciné‑Kodak, to use it. This brought to the general public the possibility of making their own motion pictures. The cost of this art form was further reduced when Kodak, in 1932, introduced 8 mm motion picture film and a camera, the Ciné‑Kodak Eight, to use it. This article tells the story of that revolution, and describes the extensive line of cameras that proceeded from it through about 1957.
Issue 5, 2024.01.16. 32 pages, 8101 words, 25 illustrations. PDF format, 1.7 MB.
The Kodak Ciné-Kodak Special 16 mm motion picture cameras
In 1933, Eastman Kodak Company introduced the Ciné‑Kodak Special professional 16 mm motion picture camera. In 1948, it was succeeded by the Ciné‑Kodak Special II. This article describes these cameras in considerable detail, including extensive discussions of various pivotal mechanisms.
Issue 2, 2017.10.29. 49 pages, 12,500 words, 36 illustrations. PDF format, 2.2 MB.
The Kodak type S lens mount and the Ciné-Kodak Special
In the mid-1930's, Eastman Kodak had a nice stable of lenses suitable for use on a number of Ciné‑Kodak motion picture cameras. But each camera model used a different lens mount, so each of the lenses had to be made in versions with all those different mounts, a logistical nightmare. To escape this, Kodak designed a "universal" lens mount for 16‑mm ciné lenses, identified as the "Type S" mount. Then, for each camera model, there would be an adapter that would allow any S-mount lens to be mounted on that camera. But, in the case of the Ciné‑Kodak Special camera, the pinnacle of the Ciné‑Kodak line, a complication involving the camera viewfinder made the new scheme a nightmare of a different kind.
Issue 1, 2019.04,04. 21 pages, 5128 words, 11 illustrations, one appendix. PDF format, 831 kB.
The film transport mechanisms of Ciné-Kodak movie cameras
In 1923, Eastman Kodak Company introduced 16 mm motion picture film and a camera, the Ciné‑Kodak, to use it. This brought to the general public the possibility of making their own motion pictures. The cost of this art form was further reduced when Kodak, in 1932, introduced 8 mm motion picture film and a camera, the Ciné‑Kodak Eight, to use it. This article describes the film transport mechanisms of those pivotal cameras and later ones of the same “dynasty”.
Issue 1, 2017.10.29. 46 pages, 12,190 words, 45 illustrations. PDF format, 2.4 MB.
Lens mounts of Kodak Ciné-Kodak movie cameras
The “home movie” era began in the U.S. when Eastman Kodak, in 1923, introduced 16 mm safety film and a practical camera to use it. Over the ensuing decades, Kodak introduced a number of 16 mm movie cameras. In 1932, Kodak introduced 8 mm movie film, and a series of cameras using that medium emerged. With a few exceptions, these cameras all had the Ciné‑Kodak “marque”, and were the beginnings of what we might call the Ciné‑Kodak dynasty. Many of these cameras (some in later versions) were arranged for interchangeable lenses, using a repertoire of different mounts. In this article we will see the various mounts and how they operate. Included is information on how features of the mounts may interact with the camera’s eye level viewfinder for control of the viewfinder field of view as lenses of different focal length are used.
Issue 2, 2017.12.31. 31 pages, 7533 words. PDF format, 1.6 MB.
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Colorimetric Characterization of Digital Camera Sensors
Digital camera sensors typically have three sets of photodetectors, with differing spectral responses. When a small area of the sensor receives a certain light, the sensors in the three sets (referred to as “channels” in this context) deliver three output values. It would be nice if this set of three values would consistently tell us the color of the light, but for the sensors we commonly encounter, it doesn’t
That makes it essentially impossible to, from a set of these values for a pixel of the image, accurately determine what color (under the representation defined for a certain color space) to record for the pixel.
It also makes complicated the matter of describing the response of the sensor (as we might look to some testing laboratory to do for us).
In this article, I discuss these interlocking issues.
An appendix discusses the reports of sensor behavior for various digital cameras published by a well‑respected testing laboratory (DxOMark) and discusses some conundrums in them.
Issue 1, 2015.10.18. 11 pages, 5285 words, 9 figures, one appendix. PDF format, 448 kB
The CIE XYZ and xyY Color Spaces
A Color Space is a completely‑specified scheme for describing the color of light, ordinarily using three numerical values (called coordinates). An important color space, defined by the International Commission on Illumination (CIE, the initials of its French name) is the CIE XYZ color space. It is widely used in scientific work, and color descriptions in other color spaces are often related to their representation in this space. A derivative of this color space, the CIE xyY color space, is often used as a way to graphically present the chromaticity of colors.
The XYZ color space itself has a fascinating genesis. Its nature, history, and role in both theoretical and practical color science are described in this article, along with that of its cousin, the CIE xyY color space.
The article begins with a review of several important technical concepts that are involved in the story.
Issue 1, 2010.03.21. 16 pages, 4465 words, 7 illustrations. PDF format, 241 kB.
The CMOS APS Digital Camera Sensor
Many digital still cameras today use a “CMOS” sensor array. The name comes from the fact that this type of sensor uses the same construction, and can be fabricated with much the same technique, as the familiar CMOS (complementary metal-oxide-semiconductor) integrated circuit chip. However, the designation also implies an architecture and readout technique dramatically different from that of the other popular sensor type, the CCD (charge-coupled device). In this article we discuss the principles and operation of an important form of the CMOS sensor, the active pixel sensor (APS) form. We also describe a specific application of the design in the sensor used by Canon, Inc. in various of its digital SLR cameras.
Issue 2, 2006.06.08. 14 pages, 4160 words, 2 figures. PDF format, 279 kB
The concept of color and color models (coordinate systems for defining a specific color); color model families: tristimulus family, luminance-chromaticity family, luminance-chrominance family; gamma precompensation; details of specific color models for computer graphics, for TV transmission, for still and moving images, including the RGB family, YIQ, YUV, YCbCr, CIE L*a*b* ("CIELAB"; no, "LAB" is not short for "laboratory"), and many others; the CIE chromaticity diagram; luma and chroma; chromaticity vs. chrominance.
Issue 8, 2005.11.08. 40 pages, 13,200 words. PDF format, 242 kB
Color temperature is a concept in which the chromaticity ("color") of a specific flavor of white light is described by reference to the chromaticity of the light emitted by a blackbody radiator at a certain temperature.
This article explains the concept and gives cautions regarding some widely-held misconceptions in this area.
Issue 4, 2005.11.08. 10 pages, 2700 words. PDF format, 976 kB
This Excel spreadsheet allows the user to calculate the near and far limits of the depth of field for focus at any specified distance; the hyperfocal distance; and the near limit of the depth of field for focus at the hyperfocal distance. Separate sheets are provided allowing distances to be stated in meters, millimeters, feet, or inches.
The format allows for the particulars of several "setups" to be entered on separate lines so that the results can be easily compared.
Issue 12, 2010.06.13. XLS format, 51.5 kB
Depth of Field in Film and Digital Cameras
Although the image of an object created by a camera is only “perfectly focused” when the object is at the precise distance to which the camera has been focused, objects at other distances (over a certain range) will have images of what we still consider “acceptable sharpness”, an honor for which we must adopt some objective, if arbitrary, criterion. The range of object distances for which this occurs is spoken of as the depth of field of the camera. It is not a physical property, merely a man‑made construct that can help the planning of photographic setups.
This article discusses the traditional concept by which depth of field is defined, quantified, and calculated, and describes an alternate philosophy sometimes used to develop a criterion of “acceptable sharpness”. It also discusses the way in which the film frame or digital sensor size of a camera influences depth of field. The related topics of depth of focus and out of focus blur performance are also discussed.
An appendix gives the equations by which depth of field can be reckoned. Another appendix discusses some of the ramifications of the use of the “depth of field calculators” widely available on‑line.
Issue 12, 2023.009.27 22 pages, 5721 words. PDF format, 122 kB
Derivation of the "Cosine Fourth" Law for Falloff of Illuminance Across a Camera Image
In a photographic system, for a given object luminance (brightness), the image illuminance on the film or equivalent declines as we move outward from the center of the image as a result of the geometric optics involved. The result is a relative darkening of the image toward its borders. If we consider a lens having certain ideal properties, it can be shown that the decline in relative illuminance goes very nearly as the fourth power of the cosine of the angle by which the object point is off the camera axis. Here we derive this relationship. We also discuss differing results given by other authors.
Issue 4, 2007.05.01. 12 pages, 3170 words. PDF format, 146 kB
Describing Digital Camera Sensor Sizes
Several curious conventions are used to describe the general size of sensors in digital cameras. We often find the size of sensors of “compact” digital cameras described with a notation such as 1/1.7” (which refers to a sensor size of about 0.32” x 0.24”). In a larger camera range, we find a sensor size described as 2/3” (that sensor size is about 0.26” x 0.35”). In a larger range yet, we may find an 0.89" x 0.59" (22.5 mm x 15.0 mm) sensor described as “1.6x”. That same sensor is sometimes described as being “APS‑C” size, or as “APS size”. In this article, we describe the premises, evolution, and definitions of these various systems of notation.
Issue 1, 2008.09.26. 7 pages, 1980 words. PDF format, 106 kB
Describing the Potency of Light
In many types of technical work it is necessary to quantify the “potency” of light. The matter is complicated by the fact that there are many distinct circumstances in which the potency of light is a consideration, each having its own physical concept, dimensionality, and units of measure.
In this article we describe these circumstances and the way in which the potency of light is quantified for each.
Issue 3, 2013.08.19. 16 pages, 3500 words. PDF format, 108 kB
Determining MTF with a Slant Edge Target
The modulation transfer function (MTF) of a photographic lens tells us how effectively the lens transfers a luminance variation in the scene (by which detail is conveyed) onto the focal plane, and in particular how that varies with spatial frequency (which we can think of as the “fineness” of the detail). This function indicates, objectively, the “resolving potential” of the lens.
We often read of the MTF being determined using a slant edge target test. In this article we review the concept of the MTF and the principles of this testing technique.
Issue 3, 2013.12.01. 11 pages, 3315 words, two illustrations. PDF format, 87 kB
Digital Camera Sensor Colorimetry
We look to a digital camera sensor to discern the color of the light landing on it and report that in some system of “color coordinates”. It does this by essentially emulating the mechanism used by the human eye to discern color. But for practical reasons, that emulation is imperfect. In most practical sensor designs, two “instances” of light having different spectrums but nevertheless having the same color but may be reported by the sensor as having different colors.
The story of this involves many concepts. Near its end, we see the motivations for, and the nature, certain compromises in practical sensor design, and we see how their adverse affects are mitigated.
Language used to describe the color response properties of a sensor is explained. Included is a discussion of the role in all this of the concept of “white balance color correction”. Extensive background review is given to several areas pivotal to the overall presentation, such as the nature of color, the concept of color spaces, and so forth.
Issue 1.1, 2010.03.15. 27 pages, 8240 words. PDF format, 188 kB
The Effect of Inserting a Flat
Glass Plate into the
Optical Path Downstream from a Lens
If a flat glass plate is inserted, perpendicular to the optical axis, into the path of rays from a lens heading to form an image, its effect is to shift the point of convergence of the rays (the point at which an image is formed) away from the lens by an amount depending on the thickness of the plate and its index of refraction. In this article, we derive the expression for the amount of this shift.
Issue 1, 2007.07.13. 4 pages, 920 words, two figures. PDF format, 107 kB
In digital photography, a convention called “35‑mm equivalent focal length” is used to allow comparison, across cameras of different format size, of the field of view implications of the use of a lens of a certain focal length on a particular camera.
This article describes the issues that are involved and the working of this convention.
Issue 1, 2009.03.25. 4 pages, 1200 words. PDF format, 78.9 kB
In digital photography, a convention called “equivalent focal length” (more precisely, “35‑mm equivalent focal length”) is widely used to allow comparison, across cameras of different format sizes, of the field of view implications of the use of a lens of a certain focal length on a particular camera. It works by describing the focal length of the lens that, if used on a 35‑mm film camera, would give the same angular field of view as the lens of interest gives on ”this” camera.
In recent times, we hear, again in connection with a lens being used on a camera whose format size is not that of a 35‑mm film camera, of its “effective f‑number”.
What might that mean? In this article, I describe one thing that is often meant.
Issue 2, 2023.11.05. 7 pages, 9800 words. PDF format, 65.5 kB.
Exposure Control in the Canon Wireless Flash System
The Canon Wireless Flash System allows freestanding Canon Speedlite flash units remote from a Canon EOS-type SLR camera to be controlled and triggered by optical signals transmitted from a master Speedlite flash unit or Speedlite flash control transmitter located at the camera. The system includes flexible provisions for adjusting the relative contribution to exposure of different flash units, including the topic often spoken of as “flash ratio setting”. In this article, we describe the system and its exposure control provisions.
Issue 1, 2006.06.12, 8 pages, PDF format, 80 kB
We often hear that “a standard photographic exposure meter [or automatic exposure system] is calibrated to a reflectance of 18% [or maybe 13%, or some other nearby number].” Sometimes the word “gray” appears in the description. What does this mean, and why the large variation in the numerical value? In this article, we look at several relevant ISO standards and see how a “standard exposure meter calibration” is implied by their interaction. In an appendix, we look into the calibration situation for Canon digital SLR cameras, as inferred from a test recommended by the manufacturer. We also discuss the related issue of incident light metering, including by way of the use of a “gray card”. A summary is included.
Issue 1, 2006.05.06. 23 pages, 6100 words. PDF format, 162 kB
Exposure Metering Modes in the Canon EOS-300D (Digital Rebel) Digital Camera
The Canon EOS-300D (Digital Rebel) digital camera can employ a number of different exposure metering modes for both ambient and (where applicable) flash components of exposure. The user has no free choice of the mode in effect. Rather, it is chosen based on the user's choice of shooting mode and other operational options. This chart shows which modes come into play under what circumstances.
Issue 6, 2004.09.17 1 page, PDF format, 40 kB
The field of view of a camera refers to the region in three dimensional space which is taken in by the camera’s view. It is basically an angular property. There are a number of ways in which its extent can be numerically stated. In this article we discuss the significance of field of view, various approaches to its quantification, and of terms used in that connection.
Issue 2, 2006.02.02 11 pages, PDF format, 114 kB
Format Size in Digital Photography
In photography, the term “format size” describes the actual physical size of the image captured by the film frame, digital sensor, or equivalent. The widespread popularity of digital photography has brought to the user community a plethora of different format sizes, most of them unique to digital photography. In this article, we review the effect of format size on a number of camera behavior and performance issues. We also debunk various misconceptions that circulate in this area, and discuss terminology used to identify a significant numerical factor.
Issue 2, 2005.09.08 17 pages, 7400 words. PDF format, 133 kB
A synopsis of this article is available here:
Format Size in Digital Photography - Synopsis
This is a synopsis of the principal topics covered by the tutorial article, Format Size in Digital Photography. Readers should be aware that, of necessity, this synopsis overlooks many important “if’s, and’s, and but’s”, and I have taken certain liberties with technical precision in the interest of conciseness. Readers wishing additional, more detailed, or more rigorous information on these topics should consult the article proper.
Issue 1, 2005.09.08 3 pages, 1160 words. PDF format, 63 kB
The Fourier Analysis Tool in Microsoft Excel
The spreadsheet application Microsoft Excel includes a tool that will calculate the discrete Fourier transform (DFT) or its inverse for a set of data. Users not familiar with digital signal processing may find it difficult to understand the scales used for the input and output data for this process. In this article we review the concept of the discrete Fourier transform, summarize how the Excel tool is used, and explain the meaning of the scales for the data.
Issue 1, 2009.03.04 11 pages, 3570 words, 5 figures. PDF format, 128 kB
A Gaffe in the ISO Standard for Photographic Exposure Meters
The international standard for photographic exposure meters, ISO 2720-1974, contains an inexplicable gaffe, leading to a curious situation regarding the exposure meter calibration constants, K and C. This article tells the story.
Issue 4, 2014.12.06. 7 pages, 2095 words, one figure. PDF format, 108 kB
The Hemispherical Receptor Incident Light Exposure Meter
Incident light exposure metering is a useful technique for planning photographic exposure in many situations. An important genre of incident light exposure meter uses a hemispherical receptor. While there are various facile explanations of what this implementation does and why that is beneficial, the underlying technical concepts are elusive.
In this article I give a concise overview of the basic operation and premises of this type of meter. Some basic background in the concept of incident‑light exposure metering is provided.
[This article is largely an excerpt from the article "The Secret Life of Photographic Exposure Metering", which provides more technical detail on the matter.]
Issue 2, 2014.08.05. 9 pages, 2690 words. PDF format, 123 kB.
The HSV and HSL Color Models and the Infamous Hexcones
The color models known as HSV and HSL (and specific color spaces based on them) are intended to provide ways of describing color that have a broad relationship to the easily‑grasped color attributes hue, saturation, and relative luminance. Almost invariably when an HSV color space is described, it is mentioned that “the color space can be described by a hexcone (a homey synonym for hexagonal pyramid)”. Similarly, we hear that the HSL color space can be “described by a bi‑hexcone” (meaning two hexagonal pyramids joined at their bases).
But these descriptions are paradoxical—the gamuts of these color spaces, “plotted” in their inherent cylindrical coordinate systems, are in fact full circular cylinders. So what might be meant by the allusion to these other, tapered solid figures?
In this article, we describe these two color models and reveal the rationales by which these unusual geometric figures are invoked as representing the associated color spaces.
The article begins with a review of the principles of color, color models, color spaces, and gamuts.
An appendix describes a “different” HSL color model used by Canon in some of its image manipulation software.
Issue 3, 2008.05.12. 30 pages, 8300 words, 10 figures. PDF format, 788 kB
The ISO Definition of the Dynamic Range of a Digital Still Camera
The dynamic range of a digital camera can be simplistically defined as the ratio of the maximum and minimum luminance that a camera can “capture” in a single exposure. But when we try to quantify this property, we find that the establishment of an explicit definition is much more complicated than it seems on the surface. International Standard ISO 15739-2003 gives an explicit definition of dynamic range for a digital still camera and a procedure for determining it. This article explains the basic concept of dynamic range and discusses some of the complications in defining it. Then, the definition given by ISO 15739-2003 is discussed in detail.
Issue 2, 2008.02.06 15 pages, 4580 words. PDF format, 129 kB
Improved Beamwidth Control in Canon Speedlite Flash Units
With the Speedlite 580EX flash unit, Canon introduced an “image size compensation” feature intended to optimize the automatic beamwidth control (the automatic “head zoom” functionality) when the flash units are used with EOS digital SLR cameras having different image sizes. However, an anomaly in the scheme put into effect an insufficient beamwidth for smaller focal length lenses.
In this article, we review the overall matter of beamwidth control, the Canon image size compensation scheme, the anomaly in the initial 580EX and its impact, and how the scheme works, without anomaly, in newer production of the 580EX and in later models. Charts are included to present the tedious details.
An appendix discusses the operation of the beamwidth control system when a Canon Speedlite 580EX II is used on a Canon Powershot SX20 IS compact camera.
Issue 2, 2011.09.01 17 pages, 4700 words, one figure. PDF format, 121 kB
JPEG Compression of Still Images
A technique known as JPEG is widely used for the compression of digital data representing photographic still images. In this article, we explain how this technique works. Appendixes give tutorial insight into several technical concepts that are involved, including the Discrete Cosine Transform (DCT), Huffman coding, and run-length encoding, and discuss the difference between reversible ("lossless") and non-reversible ("lossy") compression.
Issue 1, 2003.08.16. 19 pages, 5740 words. PDF format, 232 kB
The Kodak type S lens mount and the Ciné-Kodak Special
In the mid-1930's, Eastman Kodak had a nice stable of lenses suitable for use on a number of Ciné‑Kodak motion picture cameras. But each camera model used a different lens mount, so each of the lenses had to be made in versions with all those different mounts, a logistical nightmare. To escape this, Kodak designed a "universal" lens mount for 16‑mm ciné lenses, identified as the "Type S" mount. Then, for each camera model, there would be an adapter that would allow any S-mount lens to be mounted on that camera. But, in the case of the Ciné‑Kodak Special camera, the pinnacle of the Ciné‑Kodak line, a complication involving the camera viewfinder made the new scheme a nightmare of a different kind.
Issue 1, 2019.04.04, 21 pages, 5126 words, 12 illustrations, one appendix. PDF format, 831 kB.
The La Crosse BC-900 Battery Charger/Tester/Conditioner
The La Crosse BC-900 is a charger, tester, and conditioner for AA and AAA size rechargeable cells of the Ni-Cd and Ni-MH types. It offers extremely flexible management of its numerous functions. In this article, we review the features of this unit and give instructions for its operation.
Issue 1.1, 2006.06.25. 6 pages, 2200 words. PDF format, 78 kB
In large‑format film cameras (and smaller-format cameras whose design is derived from large‑format cameras) there are three principal types of back used: the spring (Graphic) back, the Graflex back, and the Graflok back. This article describes these three types (with illustrations) and gives insights into their implications.
Issue 1, 2007.03.31. 9 pages, 2460 words. PDF format, 225 kB
Lens Principal and Nodal Points
In discussions of photographic lenses, we often hear of the importance of the principal points and nodal points of a lens. This article describes what these are and why they are significant.
Issue 3, 2004.01.21. 5 pages, 1315 words. PDF format, 53 kB
M, X, and V on Camera Shutters
Often in connection with older cameras we see or hear of the markings "M", "X", and "V" on a lever on the shutter, or may see or hear of the flash sync connector on a camera labeled as "X". In this article, we explain the history and significance of these markings. In the process, we will visit other parts of the alphabet, including "F", "S", and "PC".
Issue 2, 2004.01.17. 4 pages, 1300 words. PDF format, 53 kB
The Mathematics of Extension Tubes in Photography
Extension tubes are devices that are placed between an interchangeable camera lens and the camera body to shift the focusing range of the camera to embrace shorter subject distances. The object is generally to achieve a greater image magnification than can be had with the lens in its normal situation. In this article we review the optical principles involved with the use of extension tubes, and give various equations useful in their application.
Issue 1, 2013.10.10. 11 pages, 2735 words. PDF format, 78 kB
The mechanics of the JPEG image encoding system
The JPEG image encoding system provides for a representation of a digital image in far fewer bits that would be required by a "straightforward" representation. The system comprises many ingenious stages. In this article, I describe the working of these stages in considerable detail.
Issue 2, 2014.06.07, 20 pages, 6525 words. PDF format, 246 kB.
Metameric Error in Digital Photography
The color of light is defined wholly in terms of visual perception. The color of an instance of light perceived by the human visual system—by definition, that is the color of the light—is determined by the spectrum of the light. Any particular spectrum will “have” a specific color. But there can be many spectrums that will have the same color, a situation called metamerism.
Ideally, a digital camera imaging system would honor this, “recording” the same color for light of any spectrum having the same color. But various compromises in sensor design make our cameras fall short of this; they exhibit some degree of metameric error.
In this article we investigate human perception of color, the nature of metamerism, the operation of digital camera sensors, and why metameric error exists. We also discuss ways in which the impact of metameric error can be mitigated, and the way in which the residual metameric performance of a digital camera sensor can be “scored”.
Issue 1, 2010.03.22. 12 pages, 3575 words. PDF format, 106 kB
A Metric for Chromaticity Difference
In many areas of photographic practice, we are concerned with the difference between two chromaticity values, especially in connection with “white balance color correction” matters. An example would be the departure of the recorded image of a “white” object from the reference white chromaticity of the color space in use, or the departure form “neutrality” of the reflective chromaticity of a “neutral target” (gray card).
In this article, the author suggests the use of the metric “du’v’” as a single-valued measure of the degree of a chromaticity difference. The metric is defined and a rationale given for its use. An appendix defines the way this metric can be calculated from the sRGB coordinates R, G, and B of the two colors whose chromaticity we wish to compare. An available spreadsheet is also described that can be used to perform this determination.
Issue 1, 2008.02.08. 9 pages, 1850 words, one figure. PDF format, 219 kB
Mosaic Sensor Arrays in Digital Photography
Many contemporary digital still cameras use a mosaic sensor array (often called a color filter array, or CFA, or a Bayer array) to develop a digital color image of a scene. In this article we describe this device, the principles of its operation, and its implications on the nature of digital camera images..
Issue 1, 2003.08.04. 7 pages, 2200 words, PDF format, 63 kB
Describing the speed of Morse code transmission
From a traffic capacity and operator proficiency standpoint it is common to specify the speed of Morse code transmission in words per minute (WPM), and of course we immediately wonder “what counts as a ‘word’ ?“
From a transmission channel standpoint, engineers are interested in the modulation rate (denominated in bauds), the reciprocal of the time resolution of the serial signal (in seconds).
In this article I discuss how these are related under a certain standard convention.
An appendix presents several related topics.
Issue 1, 2022.11.27. 12 pages, 3245 words, 3 figures, 1 appendix. PDF format, 151.8 kB
New Measures of the Sensitivity of a Digital Camera
CIPA, the technical association of the Japanese camera industry, introduced in 2006 two new measures of the “sensitivity” of a digital camera, recommended for use instead of the ISO speed rating to date used for the purpose. They are the standard output sensitivity (SOS) and recommended exposure index (REI). These new measures are also defined, as alternatives to the ISO speed, by the 2006 version of the relevant ISO standard itself. In this article, we discuss these two new measures and their significance. The article begins with background information on related topics encountered in the discussions. A summary is included.
Issue 2, 2007.08.30. 13 pages, 3900 words. PDF format, 107 kB
Norwood’s dome: a revolution in incident‑light photographic exposure metering
In the late 1930’s, Donald W. Norwood introduced a new principle of incident light photographic exposure metering in which a translucent hemispherical shell (a “dome”) collects the ambient light incident on the scene for measurement by a photoelectric cell. It was found that exposure meters following this principle could, with a single measurement, consistently develop an exposure recommendation that would be highly appropriate over a range of lighting situations, especially those of interest in cinematography and portrait photography.
Today, the preponderance of exposure meters exploit Norwood’s principle in their basic configuration for incident light exposure metering..
But it is not at all obvious, even after considerable study, just how and why meters following Norwood’s principle give this long‑acclaimed performance. In this article, we will look “under the dome” and see just what is going on.
Background is given in various pertinent aspects of the topic of exposure metering. Appendixes discuss in detail various pivotal technical issues.
Issue 4, 2023.08.22. 29 pages, 7472 words, 12 figures, 3 appendixes. PDF format, 874 kB
Oblique Astigmatism in Camera Lenses—Meridional and Sagittal MTF Response [Title changed] Updated
When presenting lens performance data in the form of a modulation transfer function (MTF) plot, we usually see separate curves for meridional and sagittal response. This primarily relates to a lens aberration called oblique astigmatism. This article discusses oblique astigmatism and the significance of the terms meridional and sagittal. It begins with a concise review of the concept of the MTF plot.
Issue 5, 2024.03.10. 21 pages, 6555 words. 16 figures. PDF format, 687 kB
On the Term “Field of View Crop Factor”
In photography, the term “field of view crop factor” is sometimes used to describe the ratio of the format size of a full-frame 35-mm camera to the format size of a particular camera of interest. This article describes the underlying technical concept and why we are interested in the factor itself. The author also suggests that the term is not appropriate, and gives his reasons for that opinion, including a critical examination of the rationale often offered by the term’s proponents.
Issue 5, 2006.05.06. 4 pages, 1500 words. PDF format, 73 kB
This Excel spreadsheet allows the user to determine the amount of blurring on the image (in terms of the actual diameter of the circle of confusion) for an object at a certain distance for focus at a different distance. Separate sheets are provided allowing distances to be stated in meters, millimeters, feet, or inches.
The format allows for the particulars of several "setups" to be entered on separate lines so that the results can be easily compared.
Issue 5, 2006.05.13. XLS format, 38.9 kB
The Packard Ideal shutter is a behind‑the‑lens shutter widely used in large‑format view cameras. It was introduced in the late 1800s and is still made and used today. This article describes the shutter, its features, and how it operates. An appendix describes, with illustrations, the detailed working of the shutter mechanism.
Issue 2, 2007.01.06. 15 pages, 4100 words. PDF format, 406 kB
Parallax Suppression in a
Target Rifle Aperture Sight
by Robert J. Burdge and Douglas A. Kerr, P.E.
With an aperture sight, often used on target rifles, the shooter looks through a small hole in a metal plate that is mounted on the rear of the rifle near the shooter’s eye, observes a front sight which is typically a small vertical post located near the front of the barrel, and adjusts the aim of the rifle until the top of that post is located on the desired location on the target. Additionally, users of these sights are always urged to position their eye so that the tip of the post is positioned precisely in the center of the field of view observed through the rear sight aperture. This is done in the interest of eliminating parallax shift between the front sight and target which would lead to uncertainty in aiming.
But we find that, as we look through such a sight and move our eye from side to side (with the aiming point of the rifle fixed), we see essentially no change in the relative position of the tip of the front sight and the target. The expected effect of parallax shift does not appear. This suggests that sight alignment, in the traditional sense, does not affect the point of aim.
In this article we look into this phenomenon. In the process, we will encounter various related matters in the fields of photographic optics and human vision. The results of both “live fire” and optical model tests are given and discussed.
An appendix presents a ray tracing exercise that demonstrates the phenomenon and its source.
Issue 4, 2007.05.30. 23 pages, 6140 words, numerous illustrations. PDF format, 311 kB
The following article is a companion to this one.
Parallax Suppression with a Target Rifle Aperture Sight—An Optical Demonstration
In the use of the common aperture sight on rifles in precision target shooting, common wisdom emphasizes the necessity for the shooter to carefully maintain his eye position so the tip of the front sight post appears centered within the circular field of view of the rear sight aperture. Otherwise, goes the wisdom, parallax shift will occur, which will disrupt the accuracy of the shooter’s aim.
A recent article by Robert J. Burdge and Douglas A. Kerr, P.E., points out that this parallax shift doesn’t seem to really occur in practice, and advances an explanation in terms of basic optical theory.
Subsequently, Kerr conducted tests in which the human eye is replaced by a digital camera in the interest of actually demonstrating the behavior involved. This article reports on these tests and discusses the results.
Issue 2, 2007.05.30. 12 pages, 3090 words, numerous illustrations. PDF format, 226 kB
This article is a companion to one listed just above.
The paraxial approximation in optical system analysis
Rigorous theoretical analysis of an optical system (even a simple lens) involves “ray tracing”, in which the path of illustrative “rays” of the light coming to the lens from the “object” being imaged is followed through the various interfaces (e.g., between air and glass) the ray encounters. This involves a number of trigonometric relationships, and thus (especially before the advent of digital computers) was quite tedious to perform.
Then, when the results are in, they often do not paint a “tidy” picture of the system’s behavior. For example, for a lens with spherical surfaces, the focal length of the lens, a parameter we are often keen to know, is generally not the same if we consider rays passing through the lens at varying distances from its center.
The painful trigonometry can be avoided, and a “tidier” (if somewhat naïve) result obtained, if we limit our consideration to rays that only depart by an infinitesimal angle from lying along the optical axis of the lens (the so‑called “paraxial” rays). This article tells the story of doing that. Appendixes give some extended algebraic exercises.
Issue 1, 2024.04.05. 19 pages, 4047 words, 5 figures, 2 appendixes. PDF format, 292 kB.
Pixel Resolution in Digital Photography
This article gives insight into a number of aspects of the concept of pixel resolution in digital photographic practice. Topics include: What do we mean by resolution, and what is pixel resolution? What is the resolution indicator in a digital image file, and what does it mean? What are resizing, resampling, and interpolation? What do publishers mean by their resolution requirements for submitted digital photographs? What is the difference between a pixel and a dot? How do we accommodate the resolution appetite of a printer?
Issue 1, 2004.11.09. 13 pages, 4300 words. PDF format, 110 kB
Photographic Exposure Metering and the Infamous “18% Calibration”
We often hear it said that photographic exposure meters (including those forming part of camera automatic exposure systems) are “calibrated to 18% reflectance” (or maybe 12.8% or thereabouts). What does this mean? In this article, we discuss what this actually means in digital photography. We also discuss the closely-related matter of “18% gray card metering”.
Issue 1, 2004.07.19. 7 pages, 1800 words. PDF format, 98 kB
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PHOTOGRAPHIC EXPOSURE METER FAMILIES
During the history of photography, there have been few aspects so fertile as that of photographic exposure meters. Hundreds of firms spawned thousands of models. Three historically-important families of exposure meters have recently come under study here, the GE "DW" series, the "Weston Master" series, and the "Norwood Director" series. Each of them is discussed in some detail in separate articles, listed below.
The GE "DW" line of photographic exposure meters
General Electric made a line of photographic exposure meters with model numbers beginning with "DW" from 1937 thorough the 1950s. They were widely used, especially by amateur photographers. In this article, I describe the evolution of this line, pointing out interesting and curious technical wrinkles that emerged along the way.
Issue 2, 2014.10.28. 14 pages, 3195 words, 6 figures, one appendix. PDF format, 241 kB.
The "Norwood Director" family of photographic exposure meters
An important family of photographic exposure meters consists of meters which in the earlier days of the family all had the name "Norwood Director". The family has a fascinating history with respect to the meters themselves and with respect to the various people and firms involved. In this article I try to paint the overall picture of this family and its story, and describe most of the meters in it.
Appendixes discuss certain technical complexities in this area.
Issue 8, 2023.08.22, 55 pages, 14,074 words, 26 figures. PDF format, 1.55 MB.
The Weston Master family of photographic exposure meters
An important family of photographic exposure meters is the Weston Master family. The series has a fascinating history with respect to the meters themselves and with respect to the firms involved. In this article I try to paint the overall picture of this family and its story, and describe the meters in it (actually starting with one that is just before the family proper). Basic background on the underlying technical theory of incident light exposure metering and other specialized technical information is given in an appendixes.
Issue 3, 2014.11.03. 27 pages, 6388 words, 21 figures, 3 appendixes. PDF format, 891 kB.
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Photography deals with light, and we are concerned in many technical ways with light and its behavior. Especially in matters of exposure, exposure metering, and the like, our discussions often involve photometry, the discipline of describing the “strength” of light. Our discussions are often hampered by inadequate or incorrect understandings of the different concepts of the strength of light and the terms, quantities and units that are involved. This article provides a concise review of photometry as it applies to photographic matters. It also gives an introduction into how the f/number of a lens affects photographic exposure.
Issue 2, 2007.12.25. 12 pages, 3600 words. PDF format, 111 kB
Polarization of Light and Polarizers
Light is a form of electromagnetic radiation, and has the property of direction of polarization. This article discusses the concept of polarization and some of its implications. Both plane (linear) and circular polarization are covered. The operation of polarizers - optical components that manipulate the polarization of light - is described, and some applications discussed. Finally, a brief introduction is given to the use of polarizers in photography.
Issue 4, 2004.09.23. 9 pages, 2600 words, PDF format, 106 kB
Principle of the Split Image Focusing Aid and the Phase Comparison Autofocus Detector in Single Lens Reflex Cameras
Many single lens reflex (SLR) cameras are equipped with an arrangement in the viewfinder known as a split image focusing aid, intended to facilitate accurate visual determination of the point of proper focus when focusing manually. In this article, we explain the principle by which this arrangement operates. We also describe another related viewfinder manual focusing aid, the microprism field, and discuss the application of the split image principle to one type of automatic focus detection system, the phase comparison system.
Issue 5, 2005.08.28. 17 pages, 4700 words, 16 figures. PDF format, 151 kB
Programmed Automatic Exposure in Canon EOS Digital Cameras
Many modern cameras, both film and digital, offer (usually as their basic mode of operation) a “programmed automatic exposure” mode. In this mode the camera, after measuring the luminance of the scene, sets both aperture and shutter speed with no further intervention on the part of the photographer. This article discusses the details of this operation as found in the Canon EOS 10D, 20D, 300D (Digital Rebel), and 350D (Digital Rebel XT) digital single-lens reflex (SLR) cameras. It also discusses the related matters of exposure compensation (exposure bias) and program shift, tools that allow the photographer to “tweak” the programmed automatic exposure control mode to deal with the special needs of a particular shot.
Issue 1, 2005.07.04. 13 pages, 4000 words, 4 figures. PDF format, 133 kB
In cartography (mapmaking) and photography, the term projection refers to the process of mapping an array of points in three‑dimensional space to locations on a flat (or flattenable) two‑dimensional surface. A projection is a particular algorithm for doing so. Any photographic process involves projection. Still, we don't often speak of projection in connection with “ordinary” photography, but we do often hear of the concept in connection with panoramic photography (photography with a large field of view). Because of the differing interests in cartography and photography, certain statements about the properties of a particular projection, applicable to one of these contexts, may not apply to the other. This is often a cause of bewilderment to those hoping to understand the technical matters involved.
In this article we introduce the concept of projection, clarify the differing outlooks of the cartographic and photographic contexts, and illustrate the implications of the use of four important projections on a certain representative situation in photographic imaging.
The article is not a treatise on panoramic photography or on the complicated issue of choosing a projection to be used as the premise for the preparation of panoramic images.
Issue 3, 2009.02.23. 22 pages, 6230 words, 10 figures. PDF format, 188 kB
The Proper Pivot Point for Panoramic Photography
When doing panoramic photography with a conventional camera, multiple, slightly‑overlapping shots of the overall scene are taken by pivoting the camera in steps, and the images are joined to make a single large-scope image. In order to be able to properly join the images, we must avoid parallax shift between them. To do so, the camera must be pivoted about the camera’s center of perspective, which turns out to be the center of the entrance pupil of the lens.
It is widely, but incorrectly, said that the proper pivot point is “the nodal point” of the lens.
In this article we discuss the optical principles involved, and demonstrate why the center of the entrance pupil is the proper pivot point.
Issue 4, 2019.04.04. 18 pages, 5561 words, 7 figures, two appendixes. PDF format, 163 kB
Quantizing and Noise in Digital Photography
In a digital camera, when we take the voltage output of an individual sensor element and convert it to digital form, a phenomenon called quantizing (often called quantization) takes place. As a result, the digital representation does not exactly represent the voltage. At the end of the digital image chain, this results in a discrepancy between the reconstructed image and the original image.
In the area of waveform‑based digital representation of speech waveforms, we sometimes characterize this discrepancy between the original data and the reconstructed data as a special kind of pseudo‑noise, quantizing noise.
Some workers suggest that this concept is pertinent to the impact of quantizing error on digital images, and that quantizing noise should be reckoned among the ingredients of noise in a digital imaging system, a notion with which the author disagrees. In any case, the process of quantizing does have an effect on how noise already present in the sensor voltage is seen in the digital representation. In this article, both these matters are examined.
An appendix discusses a similar concept followed in the field of digital video engineering.
Issue 1, 2009.02.02. 18 pages, 6100 words. PDF format, 113 kB
Replacing the Focusing Screen on the Canon EOS 20D Digital SLR Camera
Various suppliers provide alternative focusing screens for the Canon EOS 20D single lens reflex (SLR) cameras, including such focusing aids as a split-image prism or a microprism field. This article gives step by step instructions for replacing the focusing screen on the 20D digital SLR , with illustrations.
Issue 2, 2005.09.13. 8 pages, 2260 words, 7 figures. PDF format, 234 kB
Sampling, Aliasing, and the Blur Filter
The process of capturing a photographic image in digital form with a fixed number of pixels is equivalent to the sampling used in digital audio practice. This process can introduce a type of corruption in the reconstructed image knows as aliasing. This article explains some fundamental principles of the sampling process, including the impact of the Nyquist-Shannon sampling theorem. The cause and nature of aliasing is described, along with its prevention by means of a pre-sampling low pass filter (anti-aliasing filter). The blur filter, an implementation of the low pass filter in a digital camera setting, is explained. Also discussed is the concept of the digital anti-aliasing filter.
Issue 3, 2003.11.14. 4 pages, 1400 words. PDF format, 56 kB
In most methods of representing a continuous “function” (such as an audio or video waveform or a photographic image) in digital form the first step is to capture the value of the signal at regular intervals, a process called sampling. This process can be viewed as a form of (amplitude) modulation. That outlook assists us in understanding how the reconstruction of the original function from its samples works, and helps us understand the phenomenon of aliasing, which corrupts the reconstructed function in cases where the original function does not follow certain constraints. An appendix explains the concept of the power spectral density (PSD) plot, which will be encountered extensively in the article.
Issue 1, 2011.11.21. 18 pages, 4700 words. PDF format, 124 kB
We can tilt the lens of a camera in order that the plane containing objects in perfect focus will not need to be parallel to the film plane, a desirable situation for many types of work, including architectural photography. It is often said that the required relationship between lens, film, and the desired plane of object focus is prescribed by “the Scheimpflug principle”. It fact, two criteria must be satisfied, the second of which may be in terms of the classical Gaussian focus equation. However, we may instead use as the additional criterion a second principle also articulated by Scheimpflug. In this article we describe this whole situation along with the these two principles of Scheimpflug, and we show the equivalence of this additional principle of Scheimpflug to the Gaussian focus equation.
Issue 2, 2006.07.16. 18 pages, 3990 words. PDF format, 132 kB
The Secret Life of Photographic Exposure Metering
In photographic exposure metering we make some photometric measurement of the scene or its environment, from which, combined with knowledge or presumption of the sensitivity of the film or digital sensor, is determined a photographic exposure (shutter speed and aperture) we hope will fulfill our "exposure strategy".
There are many subtleties to the concept in its various forms, and many tricky details in its execution. There are many misconceptions and misunderstandings afoot about the area.
In this article I describe the principles of the various types of exposure metering and their implications and try to rectify some of the misunderstandings. The article is not a treatise on exposure metering practice.
Extensive background is given in many matters that are predicates of the process. The presentation is somewhat technically detailed, and some basic algebra is involved here and there. The various concepts are presented in layers, a given layer possibly being visited more than once, so that at any stage the reader will hopefully have all the necessary background to follow the presentation.
Issue 8, 2017.08.13. 41 pages, 11,500 words. 2 appendixes, 13 figures and photographs. PDF format, 602 kB.
Setting Camera Exposure in Terms of Ev
In the 1950s, several camera and shutter manufacturers adopted systems for setting camera exposure through a single number that reflected the joint effect of both shutter speed and aperture. This quantity eventually came to be known as exposure value (symbolized Ev). In this article we see what this is all about and how it has been supported in practice.
Issue 2, 2007.05.15. 6 pages, 1754 words, one illustration. PDF format, 106 kB
Shift of the Plane of Best Focus With Shift In Film Position
In considering the behavior of a camera, we may be concerned with how a shift of the lens-to-focal plane distance affects the distance to the object plane of best focus. In this article, we show how this can be calculated. The derivation of the relationship is given in the appendix—an opportunity for the reader to brush up on his freshman calculus.
Issue 1, 2004.10.20 7 pages, 1230 words. PDF format, 103 kB
Some Principles of Photographic Optics
In this article, we review a number of areas of optics that are especially pertinent to the field of photography, including focal length, focus, magnification, exposure, aperture and f/number, field of view, and depth of field. Basic mathematical formulas for factors of interest are given.
Issue 2, 2004.09.05. 13 pages, 3380 words. PDF format, 144 kB
The sYCC color space is an alternative representation of the “sRGB” color space, but with a special wrinkle though which it can represent a larger color gamut than the sRGB space proper. In this article we review the definition, principles, and implications of the sYCC color space.
Issue 2, 2015.07.24. 10 pages, 3039 words. PDF format, 101 kB
An important class of photoflash unit automatically controls exposure by regulating the duration of the flash output pulse based on measurement, with a photosensor on the unit, of the light reflected from the main subject. Such flash units are often described by their manufacturers and others as “thyristor” flash units. In modern flash units that also offer more sophisticated modes of exposure control, the more basic mode is often spoken of as the “thyristor” mode. In this article, we discuss what a thyristor is and why its name has come to suggest a kind of flash unit and a particular exposure control mode.
Issue 1, 2007.06.28. 9 pages, 300 words. PDF format, 90 kB
The Unsharp Mask Process in Photographic Image Processing
Unsharp mask refers to a process used in both film and digital photographic processing to increase the apparent “sharpness” of an image. In this article we explain the working of both film and digital versions of the process, and discuss the meaning of the name. The article does not attempt to teach techniques for the effective use of the process.
Issue 2, 2010.06.05. 12 pages, 3300 words, 2 figures. PDF format, 102 kB
The Canon USM (Ultrasonic Motor) Autofocus Drive System Just now indexed here!
Many lenses in Canon’s “EF” series have autofocus drive systems described as “Ultrasonic Motor” (USM) systems. There are actually a number of different systems in this classification. This article describes the construction and operating principles of the major varieties. Included is information on the mechanisms used to allow manual focusing even with the autofocus motor drive engaged (the so‑called “full time manual focus”, or FTM, feature).
Issue 1, 2011.01.04. 27 pages, 7578 words, 21 figures, one appendix. PDF format, 402 kB.
Vision Correction in Camera Viewfinders
Many camera viewfinders are equipped with a lever or knob that controls “adjustable vision correction”, primarily to allow users who are nearsighted or farsighted to obtain a sharp view of the viewfinder image without their eyeglasses. In this article, we examine how this works and learn about the unit “diopter” which is used to quantify the amount of correction in effect.
Issue 2, 2015.03.23. 8 pages, 2489 words. PDF format, 65 kB
White Balance Color Correction in Digital Photography
Variations in the chromaticity of the light under which a scene is photographed result in variations of the chromaticity recorded for different objects, often leading to an “unnatural” color appearance in the finished image as viewed. Avoiding this effect is the task of the white balance color correction process. In this article, we discuss the concepts involved, as well as some of the ways in which the process is performed in digital photography. We also discuss various “measurement tools” used in this connection. The discussion is detailed, but not mathematical.
Issue 2, 2009.12.13. 22 pages, 8080 words, three illustrations, two appendixes. PDF format, 146 kB
White Balance Diffusers in Digital Photography
When we photograph an object illuminated by light whose chromaticity does not match the “reference white” chromaticity of the color space used to record the image, then when the “published” image is examined by a viewer, familiar objects will not seem to have their expected chromaticity. To overcome this undesirable effect, we apply color correction (often called “white balance correction”) to the captured image. In digital photography, we may actually have the camera do this for us “on the fly”. In order for the camera to do so, it must know the actual chromaticity of the incident light—the light that illuminated the subject during its photography.
Although we can measure this with a specialized laboratory instrument, we can also equip the camera temporarily with a special “front end” (often called a white balance diffuser) that will equip it to make the needed measurement itself. There is considerable misunderstanding about the technical principles involved in doing so. In this article we review and explain these principles and show how they pertain to the actual workings of this technique. The article does not discuss the operation or performance of specific available white balance diffusers.
Issue 1, 2008.02.17. 12 pages, 3850 words. PDF format, 108 kB
Evolution of the optometric refractor—the DeZeng-American Optical‑Reichert dynasty
A refractor (often known as a phoropter) is the scary mask-like instrument used (in the main) to determine the prescription for vision corrective lenses. The trail to today‘s sophisticated instruments has been laid by many inventors and engineers, working through numerous industrial firms. A major thread of evolution—which we can think of as a dynasty—began in the early 1900s with the prolific inventor Henry L. deZeng II, and over the years led directly to an important family of instruments today. This article reviews this dynasty, describing in some detail all the benchmark instruments along the way.
Issue 2, 2022.05.22. 56 pages, 14458 words, 31 figures, one appendix. PDF format, 3.3 MB
The Focimeter—Measuring Eyeglass Lenses
The focimeter (also called lensmeter, Lensometer, and Vertometer, the last two being trademarks) is an instrument for measuring the optical parameters (“prescription”) of an existing vision correction lens (eyeglass lens or contact lens). Although there exist today digital readout, and wholly automatic, focimeters, in this article I concentrate on the classical manual focimeter. I also concentrate on the use for eyeglass lenses. The principles, however, are essentially the same for contact lenses.
After the instrument is introduced, background is given on various topics in lens optics and human vision correction. Then the operation of a typical focimeter is described in considerable detail. Appendixes give background in the scheme of power measurement used for vision correction lenses; describe the actual optical principles of a typical focimeter; give some history of the development of the instrument, including detailed descriptions of benchmark instruments along that path from two manufacturers; and discuss special considerations in measuring the properties of a bifocal lens.
Issue 13, 2022.08.13. 62 pages, 15,566 words, 39 figures, 5 appendixes. PDF format, 1.7 MB
The “mustache” of the American Optical M603 Lensometer
The American Optical Company Model M603 Lensometer is a focimeter, an optical instrument used to determine the “prescription” (optical specification) of corrective lenses (eyeglass lenses or contact lenses). It was made from 1938 through perhaps 1969, and was very popular among optometrists, ophthalmologists, and opticians. (Many are still in use.)
Uniquely among all American Optical focimeters (perhaps among all focimeters), the M603 (well, actually, also its short‑lived predecessor the M602) has a “mustache-shaped” plate called the lens alignment plate. There are today many mysteries about the usage of this feature.
This report first gives some background in the operation of a focimeter, in the configuration of the M603, and in the nature of the “mustache”. Then the mysteries of its usage are discussed.
Issue 1, 2022.07.22. 11 pages, 3328 words, 6 figures. PDF format, 287 kB
Plus and minus cylinder notation in ophthalmology and optometry
The prescription for a corrective eyeglass lens of the most common form describes a composite lens, one component of which is a lens whose refractive effect is uniform in all directions (called, in the vision care fields, a “sphere” lens), and the other component of which is a lens whose refractive effect is only in a certain direction (called a “cylinder” lens). We state the refractive power of these two hypothetical component lenses and, for the cylinder lens, the angular direction of its axis (its refractive power is at 90° to its axis).
The same corrective lens can be described by (a) a sphere lens of a certain refractive power, along with a cylinder lens of a certain “plus” (positive) power, with a certain axis direction, or (b) a sphere lens of a different power, along with a cylinder lens of the same power as before but of the “minus” (negative) sign, with its axis direction 90° from that before.
In writing a prescription that will describe a certain corrective lens an ophthalmologist will invariably write it describing the lens with the cylinder component in terms of a plus power. But an optometrist will invariably write it describing the lens with the cylinder component in terms of a minus power).
The story behind this odd situation is fascinating and complex, and is described in this article in considerable detail.
Issue 1, 2022.05.08. 18 pages, 26,100 words, 13 figures, one appendix. PDF format, 138 kB.
Principles of Eyeglass Prescriptions
The refractive parameters of eyeglass lenses are specified (in a “prescription”) under a model that considers the refractive effect of the lens as a combination of the effect of both a spherical and a cylindrical lens. In this article we describe this model and its underlying optical principles, and describe how the parameters are usually stated in a prescription. We also look into the fact that a given lens can have its properties stated in two different, but equivalent ways, each used in separate branches of the eye care profession.
We also learn about the “optical cross”, a graphical presentation of the overall refractive behavior of an eyeglass lens.
Issue 4, 2022.05.08 18 pages, 5725 words, 6 figures. PDF format, 243 kB
The Refractor/Phoropter—An Important Tool in Vision Correction
In the field of vision care, refractor refers to an instrument (sometimes called a phoropter, although Phoropter is a tradename) used to examine a patient to determine the optimum properties of corrective lenses used to overcome various deficiencies in his vision.
In this article we describe the traditional “manual” form of this instrument and the basic way in which it is used.
Since corrective lenses are the heart of the overall activity here, we begin with a review of some principles of lens theory.
Next we consider the notation by which the properties of an eyeglass lens are specified in a “prescription”. We also look into the fact that a given lens can have its properties stated in two different, but equivalent ways, each used in separate branches of the eye care profession, a matter that will have an affect on the design details of the refractors to be used in those two contexts.
An appendix discusses in detail one ingenious part of a manual refractor, the Jackson cross cylinder, used to optimize the parameters for astigmatism correction. A second appendix reviews how the power of a cylindrical lens in a certain direction varies with the angle of that direction with respect to the axis of the lens.
Issue 4, 2022.05.08. 44 pages, 11,780 words, 27 figures, three appendixes. PDF format, 661 kB
Tillyer’s Additive Trial Lens System
Two systems of “refracting” a person’s eyes to develop the prescription for corrective lenses (trial lenses and the refractor) place calibrated lenses in the subject’s visual path, in effect simulating the corrective lenses. In general, two or more lenses are used in cascade to compose the simulated corrective lens. Ideally, the refractive power of the combination would be the sum of the refractive powers of the individual lenses, but it doesn’t work out exactly like that, a cause of error in defining the needed corrective lenses.
In 1923, Edgar D. Tillyer, the lens design wizard of the famed American Optical Company, patented an ingenious plan by which a set of two cascaded lenses could be made “additive” with respect to to powers marked on them. This article describes this situation and the working of Tillyer’s system. The equations involved are given in detail in an appendix.
Issue 2, 2022.05.08. 20 pages, 6190 words, 6 figures, one appendix. PDF format, 412 kB.
The fluid in the eye (aqueous humor) is at a pressure slightly higher than the ambient pressure. The relative pressure is largely determined by the equilibrium between the rate of formation of aqueous humor and the rate of its drainage from the eye. Physicians long ago determined that there is a significant correlation between this pressure (the intra‑ocular pressure, IOP) and the likelihood that the patient will develop glaucoma, a serious eye disease potentially leading to almost total vision loss.
Thus there is great interest in measuring the IOP (a matter spoken of as ocular tonometry). In the usual clinical setting, there is no reasonable way to measure it directly (as, for example, with a hollow needle connected to a manometer). But many ingenious ways to measure the IOP indirectly have been developed over the years. Almost all of these instruments (called tonometers) depend on determining how the eye, at the cornea, displaces in reaction to an applied force.
In this article, I describe in some detail two of these tonometers, and mention the general principles of some others.
Issue 1, 2022.01.16. 22 pages, 5725 words, 16 figures, two appendixes.
Trial Lenses in Vision Correction
When prescribing corrective lenses (eyeglass lenses, contact lenses), the prescriber may determine the optimum parameters for the lenses with a technique involving calibrated “trial lenses” placed in an eyeglass‑like “trial frame”. The basic concept is straightforward, but there are myriad complexities involved in its actual use and working. In this article, this process and its apparatus are described in considerable detail. An introductory section gives background in some areas of lens theory and on the nature and correction of certain vision defects. Appendixes provide further detailed information on various of the topics.
Issue 7, 2022.05.08. 58 pages, 15480 words, 35 figures. PDF format, 882 kB
The Vertex Power of Ophthalmic Lenses
The ability of a lens to converge or diverge rays of light that arrive on separate, parallel paths is quantified as the refractive power (or just power) of the lens. In most optical work, the power is defined as the reciprocal of the focal length of the lens. In the case of ophthalmic (vision correction) lenses, the “rated” power is the reciprocal of the back focal length of the lens, a different quantity. The power reckoned that way is called the vertex power of the lens. The rationale for the use of this convention has been written of ad nauseam, but rarely is the basic justification for it clearly revealed. This article seeks to do that.
The article also discusses the use of a focimeter to determine the vertex power of ophthalmic lenses, including some special conditions pertaining to bifocal lenses.
Issue 6, 2010.12.07. 27 pages, 7890 words 12 figures, two appendixes. PDF format, 147 kB
Music and electronic music, film, and video
MIDI - The Musical Instrument Digital Interface
The Musical Instrument Digital Interface (MIDI) can link together, electrically, various entities involved in the generation, storage, or execution of musical performances. This interface is the centerpiece of an entire complex paradigm of note‑oriented digital representation of musical performances. This paper reviews the basic concepts of this interface, of the paradigm it spawned, and of the related matter of the Standard MIDI File, a format for storing in a computer file the MIDI instructions for executing a musical performance. It also discusses the related concepts of MIDI‑oriented musical notation software, the MIDI sequencer, and MIDI interface hardware. The “MIDI language”, and its repertoire of MIDI messages, is discussed, with full detail, in an appendix.
Issue 7, 2009.03.09. 33 pages, 9560 words, one appendix. PDF format, 174 kB
We may wish to be able to “observe” the MIDI message streams emitted by various electronic music programs in our computer, such as scoring programs or MIDI editors, perhaps in connection with trouble shooting. Various software tools (“MIDI monitors”) allow these message streams to be captured, parsed, decoded, and displayed and/or printed for us. Their use is sometimes complicated by a gender issue at the computer’s internal (logical) MIDI interface. In this article, we describe a typical MIDI monitoring tool (MIDI Ox); discuss the gender issue, and explain how it can be overcome; and give basic guidelines for the use of MIDI Ox.
Issue 3, 2008.09.20. 22 pages, 6080 words, 5 figures, 3 appendixes. PDF format, 241 kB
Various “electronic” music activities inside a PC involve the transmission between entities of “MIDI message streams”, streams of coded messages that describe a musical performance. The flow of these streams from one entity to another is not over the traditional MIDI electrical interface, but rather over a “logical interface”, similar to the ones between applications and I/O devices such as printers and keyboards (the overall arrangement of which can be described as “MIDI plumbing”). Because of the asymmetry of this interface, there arises the concept of entity gender, which may impede us from arranging certain useful information flows. In this article, we describe this architecture, explain the limitations it imposes, and discuss various ways to circumvent those impediments.
Issue 2, 2008.09.20. 12 pages, 3390 words, 4 figures. PDF format, 177 kB
The SMPTE 27.97 fps drop-frame video time code system
SMPTE time codes are used to identify specific “points” in a video recording or film to a precision of the time of one frame, the smallest unit by which film or video recordings can be edited, trimmed, and so forth. The time codes may be embedded in the video tape or film or in the digital representation of the “production” in an editor. Musical notation programs intended for use in scoring for video productions often use these time codes as a way of precisely coordinating the music with the video itself. The structure of the time codes there is dependent on the frame rate of the production.
A common frame rate for video recordings, following from the North American analog TV broadcast format in use since the advent of color television broadcasting, and still one of the options in the current digital television broadcast system, is nominally 29.97 fps (frames/second). With a non‑integral number of frames per second, a straightforward time designation system (working in terms of integral hours, minutes, seconds, and frames) is not feasible. Rather, for this frame rate, a rather clever but tricky scheme is used. This article describes that scheme.
An appendix explains where this peculiar frame rate came from. A second appendix shows the details of the cyclic time discrepancy of the system. A third appendix describes an algorithm that can be used to convert time to hours:minutes:seconds;frames notation under this time code system. Other appendixes cover related matters, including the handling of time code matters in the musical notation program Overture 5.
The article only discusses this time code system from an abstract standpoint; there is no discussion of how the time code might be physically embedded in a film or video medium.
Issue 4, 2018.12.29. 26 pages, 7900 words, five appendixes. PDF format, 136 kB.
U-verse telecommunication service, offered by AT&T through its operating telephone companies in many areas, uses a single very high speed digital subscriber line (VDSL), or a comparable fiber link, to deliver to a residence telephone service, high‑speed Internet access, and television programming. The system design provides great flexibility in the kinds of wiring over which signals may be carried between different system devices within the premises, facilitating deployment of the service. In this article, we review the basic concepts, architecture, and features of this service, with emphasis on these various interconnection modes. The story of a U‑verse installation at the author’s home is given. An appendix gives technical details of the VDSL transmission system used in one form of the U‑verse service.
Issue 2, 2009.06.05. 23 pages, 7060 words, five figures. PDF format, 280 kB
Dallas Telephone numbers 1915‑1961 NEW, revised
The period from perhaps 1910 through 1927 was a pivotal and dynamic one for the local telephone industry in the United States. Quite commonly during that era, in a city there would be two or more competing local telephone companies, each with their own network, there often being no way a subscriber of one service could call a subscriber of the other(s). Almost always, those two operations merged, ultimately resulting in subscribers of either of the original services being able to call any subscriber in the city, regardless of their original service.
Usually, by the end of that era, economic realities resulted in the two or more companies merging in some way and then moving toward operational consolidation of their respective networks. Often at about the same time, telephone service was being converted from a “manual” basis to a “dial” basis, which of course introduced its own complications. One manifestation of this was often very “interesting” schemes of telephone numbers, both as they were dialed and as they were presented in print.
One particularly interesting case is that of Dallas, Texas, a case the author recently studied extensively. This article summarizes the findings of this study, actually extending the view through 1961, by which time the telephone numbers in Dallas had (almost) reached their “ultimate” configuration.
Issue 2, 2024-10-06. 12 pages, 3601 words, two figures, four appendixes. PDF format, 177.8 kB.
The detached contact system for telephone switching circuit schematic drawings NEW
Electromechanical telephone switching systems are extraordinarily complex, and the schematic drawings that define their circuits are nightmarish. In the early 1950s, the Bell Telephone System introduced a new scheme for these drawings, known as the “detached contact schematic system.”
The new drawing system allowed much more clearly the visualization of the circuit paths by which the circuit operated than with the previous drawing system. The labor required to make and revise drawings under this system also was substantially less than with the prior system.
The following articles describe this system in two levels of detail.
The detached contact system for telephone switching circuit schematic drawings [The short article] NEW
In this article, the important principles of the detached contact schematic system are described.
Issue 1, 2024.05.i8. 8 pages, 2094 words. 5 figures. PDF format, 668 kB.
The detached contact system for telephone switching circuit schematic drawings: the longer story [The long article] NEW
In this article, the important principles of the detached contact schematic system are described, with many details, The historical context of the evolution and introduction of the system are also described.
Issue 2, 2024.05.i8. 20 pages, 5099 words. 14 figures. PDF format, 1.7 MB.
The first North American mobile telephone system
The first general-availability mobile telephone system (in the sense of a system that extended the telephone network to mobile users) in North America was introduced by the Bell Telephone System in 1946. It was called the Mobile Telephone System (MTS) and had two “versions”, one operating in the 30-50 MHz band and one in the 155 MHz band. There were a limited number of channels allocated, and even in a large city not all of them could be used, owing to the need to reserve some for nearby cities. There was no short‑distance frequency reuse, such as we have today in the various cellular systems. As a result, in the typical large city, there could only be perhaps 12 mobile telephone calls in effect at any time. The system was wholly manual, the services of a special operator being required for both incoming and outgoing calls. This article describes the essential features of this system and its implementation. An appendix describes in detail the operation of the ingenious electromechanical selector used to recognize an incoming call for a mobile station.
Issue 1, 2015.11.16. 26 pages, 7285 words, one appendix, 8 figures. PDF format, 1.27 MB.
The hybrid coil circuit in telephone transmission systems Editorially revised
In applying amplification to a telephone circuit in which speech signals travel in both directions through a single electrical circuit (a so‑called “two‑wire” circuit), we must be able to separate the two directions of signal travel so that each can be amplified by a separate amplifier, while not allowing any path “around the loop” that could lead to oscillation. This need is traditionally met by an ingenious passive circuit known as a “hybrid coil circuit” (often called just a “hybrid”).
In this article, I first give some context for that need. Then I examine the properties of the circuit as a “black box”. Then I show classical implementations of the circuit, and describe how they do what they do.
Finally, I discuss important applications of the circuit in telephone transmission beyond the original context, and in telephone sets themselves.
Issue 3, 2024.01.15. 22 pages. 6351 words, 17 figures. PDF format, 439 kB.
Manual Telephone Switching Substantially revised
In the U.S., until about 1920, telephone switching was done with switchboards operated by human operators, an arrangement called manual switching. In the forthcoming years, this arrangement was progressively superseded by automatic switching, in which the subscribers used a dial to tell a switching machine the number they wanted to reach.
By 1960, the preponderance of U.S. telephone service was on an automatic (“dial”) basis, but some manual switchboards continued in use well beyond that. (The last Bell Telephone System manual switchboard in the state of New Jersey was retired in the mid 1960s. I had the privilege of attending its dismantlement.)
It is tempting to think that the manual telephone switching system was “primitive”, but it was far from that. There was enormously detailed, clever, and precise work done at the system engineering, circuit design, equipment design, manufacture and installation, and operational protocol standpoints.
In this article, I try to give the reader some idea of the basic (and some not‑so‑basic) concepts of the sphere of manual telephone switching, and in the process, perhaps give some idea of what a wondrous creature it was.
Issue 7, 2024-11-13. 69 pages, 19,829 words, 33 figures. PDF format, 4.7 MB.
Multi-party telephone lines—note
The following two articles discuss this topic. The first of them is extremely detailed and quite lengthy.
As to the reader primarily interested in the central technical issue here, how are the separate parties on a multiparty line "rung", the second article, which is basically limited to that issue (but which still has substantial background material on the overall topic), may be more to their liking.
Message registers in telephone switching systems NEW
For many years, telephone companies in many cities offered subscribers a service plan called message rate service. Under this plan, the subscriber paid a monthly charge for basic local telephone service, which included the ability to make (each month) a certain number of local calls (perhaps 50 or 75). Calls beyond that quota were charged for at perhaps $0.05 each.
In elctromechanical telephone switching systems, the completed local calls made by each subscriber having this type of service were counted by elctromechanical counters called message registers. A number of ingenious circuit schemes were used to operate these, a matter that was complicated by the common use of 2-party lines, where two subscribers’ telephones were connected in parallel to a single pair of conductors to the central office.
This article describes in fair technical detail these ingenious circuit schemes. Illustrative schematic circuits are shown, often simplified to best meet the needs of the discussion.
Issue 1, 2024-11-11 21 pages, 6297 words, 9 figures. PDF format, 467 kB.
Multi-party telephone lines Substantially revised
A multi-party telephone line (known to the general public as a “party line”) uses a single pair of conductors (today usually in a cable) from the telephone central office to serve two or more subscribers’ “stations”. The motive is to spread the capital and maintenance cost of the cable pair, and the equipment associated with it at the central office, over two or more subscribers’ service, allowing for lower rates than for an individual line (a single‑party line, often called by the general public a “private line”).
The technical arrangements for this type of service are varied and ingenious. In this article I describe many of these.
Topics covered include: the principle of multi‑party lines; basic telephone line operation; alerting (ringing) the various parties; numbering plans for multi‑part lines; identifying the calling party; noise considerations affecting the design of ringing systems; construction and operation of illustrative telephone ringers; and operation of manual and dial switching systems for multi‑party lines
Issue 6, 2024-06-14. 76 pages, 20,549 words. 37 figures, three appendixes. PDF format, 1.8 MB.
Ringing in multi-party telephone lines Substantially revised
A multi-party telephone line (often called just a “party line”) uses a single pair of conductors (today usually in a cable) from the telephone central office to serve two or more subscribers. The motive is to spread the capital and maintenance cost of the cable pair, and of the equipment associated with it at the central office, over two or more subscribers’ service, allowing for lower rates than for an individual line (a single‑party line, often called by the general public a “private line”).
A major issue in the implementation of this principle is how to alert (“ring”) a specific party when an incoming call is for that party. Many different schemes emerged over the years, and several eventually came into widespread use.
This article discusses these multi-party line ringing systems.
Issue 3, 2024-06-13. 19 pages, 5841 words. 10 figures. PDF format, 389 kB.
The origin of the 1.42 unit stop element in the North American 5‑bit teletypewriter system
The teletypewriters commonly seen in police stations, newsrooms, airport operations offices, corporate communication centers, and the like for many years used a 5‑bit character code and operated over a binary channel in bit‑serial form, in what would be called in today’s taxonomy of data communication the asynchronous mode (but “in the day” it was described as the “start‑stop” mode).
Each character comprised 7 sequential binary elements; the first six (the “Start element” and five “Information elements”) had the same duration, but the last one (the “Stop element”) had a duration 1.42 times the duration of the earlier intervals.
Why this odd value?
In this article, the author gives his opinion on the origin of this value, based on authentic historical documents he had reviewed in the 1960s.
Considerable background on the signal involved is provided.
Issue 3, 2023.08.11. 12 pages, 3486 words, 8 figures. PDF format, 435.8 kB.
Operation of traditional coin telephones
Telephone‑company provided coin‑operated telephones (“payphones”) were at one time ubiquitous around the world, where they were an important part of the culture.
Various schemes of operation were in use over the years in various of the world regions, and the technical aspects were complicated and intricate.
In this article, I identify several “mainstream” modes of service and operation for coin telephones as followed in the US and Canada, generally applicable up through perhaps 1960, and many of its principles beyond that, and explain their operation in some detail.
Emphasis is on operational and circuit principles rather than on the physical construction and appearance of the telephone sets (although there is some attention to those aspects).
Pertinent background is given on the telephone system infrastructure within which these telephones operated.
Appendixes cover in further detail various of the topics.
Issue 16, 2023.11.22 106 pages (good grief!), 26,900 words, 77 figures. PDF format, 3.75 MB.
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THE PANEL DIAL TELEPHONE SWITCHING SYSTEM
The panel dial system was a very complex telephone switching system developed by American Telephone and Telegraph company in the 1910s. It came to be the mainstay of the Bell Telephone’s System’s massive program, from the 1920s on, of mechanizing telephone service in many of the largest cities in the United States. The following series of articles cover the system and various special contexts of its operation, the first one the system itself.
The panel dial telephone switching system
In the 1910s, AT&T, the parent of the Bell Telephone System, anxious to reduce the stupendous labor costs of manual telephone switching (especially in large metropolitan areas), and realizing that the most prominent available switching system (the Strowger system) had serious limitations of its use in such areas, undertook the development from the ground up of a switching system based on many entirely new concepts.
This system, the panel dial switching system, came to be the mainstay of the Bell System’s program of mechanizing telephone service in many of the largest cities in the U.S. In this article, we will learn of the evolution of this system, of the unique mechanisms around which it revolves, and of the implications of its basic operational principle, known as common control. Considerable detail in system operation is given, although not usually at the circuit level, except where necessary to illustrate an important concept.
Issue 6, 2018.06.15. 83 pages, 27,200 words, 37 figures, one appendix. PDF format, 2.8 MB.
The Panel Dial Telephone Switching System—Interoperation with Manual Switching Systems
The panel dial system was a very complex telephone switching system developed by American Telephone and Telegraph company in the 1910s., It came to be the mainstay of the Bell Telephone’s System’s massive program, from the 1920s on, of mechanizing telephone service in many of the largest cities in the United States. Prior to mechanization these cities were served by switching systems using large manually‑operated switchboards.
During the conversion process in a given city, which might take a decade or more, elaborate provisions were emplaced to allow the seamless interoperation of the new mechanized (“dial”) systems with the existing manual systems, allowing subscribers served by either kind of system to reach subscribers served by the other kind in a straightforward way.
This article discusses the most widely used of such arrangements in some technical detail. Included is a detailed discussion of a telephone signaling system (the “PCI pulsing system”) that was developed to support these interoperation arrangements but which then went on the have a life of its own elsewhere in the telephone network.
Issue 4, 2018.06.18. 47 pages, 12,400 words, 27 figures. PDF format, 2.0 MB
The Panel Dial Telephone Switching System—Tandem Switching
The panel dial system was a very complex telephone switching system developed by American Telephone and Telegraph company in the 1910s., It came to be the mainstay of the Bell Telephone’s System’s program, from the 1920s on, of mechanizing telephone service in many of the largest cities in the U.S. and Canada. Prior to mechanization these cities were served by switching systems using large manually‑operated switchboards.
Tandem switching refers to the concept that a call from one central office to another is switched at an intermediate switching point, called a tandem office. The principal object is greater efficiency in the usage of interoffice trunks.
In the context of the panel dial switching system, two tandem switching schemes were employed, both using the same unique switching mechanism used in the panel dial system itself. This article describes both.
The article begins with a summary of the principle of tandem switching, and then gives a concise description of the panel dial system itself.
Issue 1, 2018.06.15. 28 pages. 8600 words, 15 figures. PDF format, 1.0 MB.
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Rotary telephone dials—two families—their looks and sounds RECENTLY NEW, this issue revised editorially and expanded
The “rotary” telephone dial was once ubiquitous in our telephone experience. In the US and Canada, most of those fell into two different families, with substantial differences in the principles of their mechanisms. There is a prominent visual clue that lets us distinguish between the families. But they also make dramatically different sounds during their operation.
This article describes the construction and operation of the two types of mechanisms, and tells how they get their distinctive “looks” and “sounds”.
Issue 3, 2024.02.21. 19 pages, 4782 words, 12 figures. PDF format, 1.3 MB.
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THE STEP BY STEP TELEPHONE SWITCHING SYSTEM
The step-by-step telephone switching system (as it is known in the Bell Telephone System; the “Strowger” system elsewhere) was the earliest “mechanized” telephone switching system to receive broad acceptance, and it remained important for many decades.
This series of articles covers many aspects of that system. The initial ("master") article gives a detailed overview of the systems., The following articles each discuss, in detail, including at the “circuit” level, one of the three kinds of switches around which the system revolves, and then several other aspects of system operation.
The step-by-step telephone switching system: Overview
First, the history of the system is reviewed. Then the architecture of the system, and the unique switch mechanism it utilizes, are discussed. The overall working of the system in handling calls is discussed in considerable detail, although not at the “circuit” level. Background is given that will be common to the companion articles.
Issue 2, 2019.12.20. 47 pages, 13,100 words. 25 figures. PDF format, 1.5 MB.
The step-by-step telephone switching system: The line finder switch
The step-by-step telephone switching system (as it is known in the Bell Telephone System; the “Strowger” system elsewhere) was the earliest “mechanized” telephone switching system to receive broad acceptance, and it remained important for many decades. This is one of a series of articles on this system, and it describes the line finder switch, which is used in the first stage of the switching network. The basic functions of the switch are summarized, its basic operation is described, and an illustrative circuit schematic drawing is used as the basis for a detailed description of its operation.
Issue 6, 2020.10.22. 34 pages, 9814 words. 18 figures. PDF format, 1.4 MB.
The step-by-step telephone switching system: The selector switch
The selector switch is used in all the "interior" stages of the switching network. The basic functions of the switch are summarized, and an illustrative schematic drawing is used as the basis for a detailed description of its operation.
Issue 2, 2019.12.20. 20 pages, 5430 words. 7 figures. PDF format, 535 kB.
The step-by-step telephone switching system: The connector switch
The step-by-step telephone switching system (as it is known in the Bell Telephone System; the “Strowger” system elsewhere) was the earliest “mechanized” telephone switching system to receive broad acceptance, and it remained important for many decades. This is one of a series of articles on this system, and it describes the connector switch, which is used in the final stage of the switching network. The basic functions of the switch are summarized, and an illustrative schematic drawing is used as the basis for a detailed description of its operation.
Issue 4, 2019.12.20. 26 pages, 7745 words, one appendix. 8 figures. PDF format, 621 kB.
The step-by-step telephone switching system: handling of toll calls
In the 1920s and 1930s, the US had a well‑developed, and very complex, system for handling long distance (“toll”) telephone calls, much of it operated by The Bell Telephone System.
Step by step (SXS) switching equipment played two major roles in that scheme. Even during the era in which connections through the “interior” of the toll network were set up with manual cord switchboards, the completion of a toll connection to a subscriber served by an SXS system was done with a special part of that system, using special versions of the SXS switches.
Then as the system evolved, special types of SXS switching equipment were used in the interior of the toll network, allowing the toll operator who initially handled the call to, by dialing, set up the entire toll connection all the way to the called station.
These SXS switching arrangements use control and signaling arrangements quite different from those of the SXS equipment used for local calls. These in part arose to support special modes of call handling traditionally used in the long distance service.
In this article we get an insight into how these SXS switching arrangements worked. It begins with extensive background on the surrounding context. The basic overall architecture of a toll call, as of the period of interest, is shown. Then the two switch trains involved are described in detail from a functional viewpoint. Next the signaling and control protocols are described. Finally, the features supporting several specialized requirements are described.
Issue 1, 2020.04.06. 29 pages, 7525 words. 13 figures. PDF format, 619 kB.
The step-by-step telephone switching system: Reverting calls Extensively revised and expanded
In a multi‑party telephone line (often called by civilians a “party line”), two or more subscribers’ stations are connected to the same pair of conductors to the central office (the “line”). The point is to spread the considerable cost of the line over several subscribers’ service, allowing service to be given at a lower rate.
If a subscriber served by a multi‑party line attempts (probably unwittingly) to call another subscriber on the same line, the call cannot be completed in the normal way. For one thing, the called line is already busy, and so the switching system will not gladly connect to it.
Such a call, if it can somehow be completed, is called a reverting call, because the connection “reverts” to the line on which the call originated.
In the step‑by‑step switching system, various special provisions for completing such calls were in wide use. In this article, we describe their principles and some of the details of their operation. Considerable background is given on pivotal topics.
Issue 2, 2024-10-02. 29 pages, 8025 words, 14 figures. PDF format, 541 kB.
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The Teletype Corporation receiving transmitter distributor
In traditional teletypewriter nomenclature, a transmitter is a reader of perforated paper tape with an output in electrical (or mechanical) parallel form, not in the form of a serial teletypewriter signal. A transmitting distributor takes a parallel signal and serializes it into a serial teletypewriter signal. A receiving distributor takes such a serial signal and deserializes it into parallel form so that it can be decoded and then (usually) printed.
Ensuite, a transmitter distributor is a unit that reads a perforated paper tape and delivers a serial teletypewriter signal.
But a unit that looks like a familiar style of transmitter distributor, used in certain message encryption systems, has the paradoxical name “receiving transmitter distributor”. What might that mean?
It actually in effect performs both receiving distributor and transmitting distributor functions. But it also reads an encryption keytape (which carries a string of random 5‑bit “characters”) and (aided by a single external relay) performs the classical regenerative repeater function and as well the classical “Vernam” encryption “mixing” for either encryption or decryption.
This article describes the operation and use of these special units. Background is given in important topic areas.
Issue 3, 2023.07.31 25 pages, 8084 words, 11 figures, 2 appendixes. PDF format, 783 kB.
THE WIRELESS INSTALLATION ON R.M.S. TITANIC
The luxury steamship R.M.S. Titanic, the largest ocean‑going passenger ship afloat at the time, sank on April 15, 1912, while on her maiden voyage, after striking an iceberg, resulting in the loss of over 1500 lives. But the fact that she was equipped with a (for the time) up‑to‑date wireless (radio) installation is credited with the saving of many lives, by bringing other ships fairly promptly to her aid.
The following two articles relate to that installation.
The wireless installation of R.M.S. Titanic
The luxury steamship R.M.S. Titanic, the largest ocean‑going passenger ship afloat at the time, sank on April 15, 1912, while on her maiden voyage, after striking an iceberg, resulting in the loss of over 1500 lives. But the fact that she was equipped with a (for the time) up‑to‑date wireless (radio) installation is credited with the saving of many lives, by bringing other ships fairly promptly to her aid. This article reviews in detail many aspects of this installation.
In order to provide background for the discussion, the article includes introductions to pivotal technical aspects of the wireless transmitters of the era. An appendix compares and contrasts the wireless installation on Titanic with that of her sister ship, R.M.S. Olympic, the two installations being often confused.
Issue 1, 2018.10.19. 31 pages, 8850 words, 15 figures, one appendix. PDF format, 891 kB.
The wireless key of R.M.S. Titanic
The luxury steamship R.M.S. Titanic, the largest ocean‑going passenger ship afloat at the time, sank on April 15, 1912, while on her maiden voyage, after striking an iceberg, resulting in the loss of over 1500 lives. But the fact that she was equipped with a (for the time) up‑to‑date wireless (radio) installation is credited with the saving of many lives, by bringing other ships fairly promptly to her aid.
Not surprisingly, students and aficionados of the wireless technology of that era often focus on the installation on Titanic. And collectors of, and experts on, antique telegraph keys often call attention to specimens of a certain type of Marconi key as being the “type used on Titanic”. But there are questions, yet unanswered (at least to the knowledge of the author), as to why this type of key was used with the kind of transmitter believed to have been used on Titanic. This article reviews this conundrum, and concludes that this belief is correct. It also discusses a related conundrum regarding the matter of the keying circuit used on Titanic.
In order to provide background, the article includes introductions to pivotal technical aspects of the wireless transmitters of the era.
Issue 2, 2019.12.18. 23 pages, 6638 words, 18 figures. PDF format, 730 kB.
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Why was the Western Electric 500D telephone set called that? Revised with corrections
For many generations of telephone sets used in the Bell Telephone System, made by their internal manufacturer, Western Electric Company, the basic units had base apparatus codes (“model numbers”) that ended with “A” (e.g., 302A) if the set had no dial and with “C” (e.g., 302C) if it had a dial with what eventually was the most common of three arrangements of numbers and letters.
In about 1950, the Bell Telephone System (and Western Electric) introduced a new family of general‑purpose telephone sets, called the “500 type”. This became the mainstream type of Bell System telephone set for many years.
But for much of the life of this family, the base apparatus code for a set with no dial was 500C, and for ones with a dial (by then only one arrangement of digits and letters was common), 500D (not 500A and 500C, as we might have expected).
This unexpected situation came about through a fascinating story of the evolution of this telephone set family in its early years—a literal “war story”. This article tells that story.
Issue 3, 2024-11-03. 6 pages, 1685 words, one figure. PDF format, 150 kB
The Varley loop and Murray loop tests for fault location in telephone circuits
Metallic (“copper”) telephone lines are subject to many kinds of electrical faults. A conductor may come “open”; the two conductors of a pair may become “crossed” (short‑circuited). One conductor of a pair may become “grounded”, or may become crossed with a conductor of another pair.
For over 100 years before the availability of modern fault locating systems, ingenious schemes for locating the faults, based on specialized combinations of precise resistance measurements (typically made by special adaptations of the Wheatstone bridge), were in widespread use.
Important among these schemes was one called the “Varley loop”, which actually refers to a family of closely‑related measurement techniques. Another similar family of tests are called the “Murray loop” tests. This article describes these tests and the instruments by which they were traditionally made.
Issue 2, 2021.09.03. 21 pages, 5250 words, 13 figures. PDF format, 476 kB
Insulin Pens and Their Mechanisms
Several types of insulin intended for injection by the diabetes patient are available in a convenient disposable administration device called an insulin pen. In three popular types, the Novo Nordisk FlexPen and FlexTouch pen and the Eli Lilly KwikPen, the device is dispensed pre‑filled with 3 ml of insulin solution, corresponding to 300 international units (IU) of insulin, which may be used for numerous “shots”. For each shot, the user attaches a disposable needle and sets the desired dose with a knob carrying a scale marked in IU. Then, after insertion of the needle at the injection site, the user presses an operating plunger or actuating button, accurately delivering the preset dose. This article describes these three popular types of insulin pen and discusses in detail, with illustrations, the operation of their ingenious and intricate mechanisms.
The reissue to Issue 3 was made principally to include information on the Novo Nordisk FlexTouch pen, recently introduced. The reissue to Issues 4 and 5 primarily made editorial improvements.
Issue 5, 2015.11.30. 34 pages, 9397 words, 27 figures. PDF format, 380 kB
The FreeStyle Libre 14‑Day continuous glucose monitor system
The FreeStyle Libre 14‑Day continuous glucose monitor system (CGM) measures a diabetes patient’s glucose concentration every minute with a small. disposable sensor (about the size and shape of a poker chip) adhesively fastened to the patient’s upper arm, with a small probe extending through the skin.. A record of the measurements at 15‑minute intervals (for 8 hours) is retained in the sensor. The readings can then be picked up, via near field communication (NFC), with either a small “reader” or by a smartphone equipped with a special app, and displayed as a graph and in other ways.
The sensor must be replaced every 14 days, normally done by the patient. The process is fairly simple for the patient, but “behind the curtain” it involves a complex process of assembling and preparing the sensor and then emplacing it on the patient’s arm.
In this article I describe the system and its features and overall operation, but emphasis is on a detailed discussion (with numerous photos) of the process of assembly, preparation, and emplacement of a sensor.
Issue 3, 2020.08.12. 27 pages, one appendix, 7120 words, 22 figures. PDF format, 582 kB.
The SkyAngel 911FD 4G personal alarm system
The SkyAngel 911FD 4G personal alarm system is a small teardrop‑shaped unit ordinarily worn around the user’s neck on a lanyard. If the user presses a large button on the face of the unit, the unit places a cellular call to “911”, and when the emergency call taker answers, the user can communicate over a two-way speakerphone. The unit will operate essentially anyplace there is cellular service (from any of several carriers).
The unit includes a fall detector, and if the user falls, the unit automatically initiates a call to 911. (The user has the option of aborting that call if this is a “false alarm”.)
Elaborated variants of the unit provide further features, including the ability to place emergency calls (and send emergency text messages) to several correspondents.
This article describes the unit in some detail and discuses various of its features and their ramifications.
Issue 1, 2022.08.03. 12 pages, 3700 words, 2 figures. PDF format, 207 kB.
Mathematics, science, and engineering
We often hear, for example, that in a certain population, “80% of the wealth is held by 20% of the population”. (Almost always, by the way, with those particular numbers.) We hear the more generic formulation, “In many natural or societal situations, 80% of the overall outcome results from 20% of the causes.”
This “situation” is often called the “80-20 rule”. It is often used to “describe” a certain inequality of income, or wealth holdings, or the like, and is often thought to widely apply to such matters. But there are many misunderstandings about what this means. For example, in the matter of wealth, does this “description” actually completely define a certain “distribution of wealth”? And, if so, is that distribution of wealth “typical” for modern societies? This article looks into many aspects of this matter.
Issue 1, 2016.01.26. 15 pages. 3680 words, 6 figures. PDF format, 195 kB.
We might read that some community, as a result of a severe series of rainstorms, was hit by a “100‑year flood”. That sounds like a pretty bad one. But just what does that expression mean?
In this article, I describe what is the usual formal definition behind that description, and discuss some if its implications. An appendix gives an equation used in the related calculations.
Issue 1, 2022.01.20. 5 pages, one appendix, 1267 words. PDF format, 59 kB.
Dimensional Analysis—A Tool for Guiding Mathematical Calculations
In converting quantities from one unit to another, we may know the applicable “conversion factor” but be uncertain as whether to multiply or divide. The same uncertainty often arises in other basic mathematical calculations, such as those involving distance, time, and velocity. A technique called “dimensional analysis” can give foolproof guidance in these cases, and can even help us develop the formula needed to determine a certain quantity. This article describes the principles involved and illustrates the practical application of the technique.
Issue 1, 2010.02.06. 8 pages, 1850 words. PDF format, 78 kB
The role of “generator inertia” in the electric power generating system New
In each of the four distinct “power grids” (formally, “interconnections”) serving the United States and Canada, most of the electrical power has traditionally come from turbine‑driven synchronous alternators (generators). These are inherently interlocked to operate at precisely the same frequency (the frequency of the grid), and all regulate their operation to deliver their appropriate quota of power into the grid while operating at such a speed that this frequency is as intended (60.0 Hz).
If a major power station on the grid unexpectedly has to suddenly stop operation, its contribution must now be picked up by the other participants. But the nature of turbine-driven alternators is such that they cannot do this “instantaneously”. The result is that, for a short period, the speeds of the alternators (and thus the frequency of the grid) will “dip”, not an ideal situation. But mitigating the slow response of the turbine‑driven alternators is the fact that each one stores, in its spinning rotor, a substantial amount of energy in mechanical kinetic (“inertial”) form.
This energy is inherently and immediately contributed to the grid (at every such power station) without any action required on the part of the control systems. As a result, the “grid frequency dip” that might otherwise occur is significantly reduced.
Today, though, a substantial part of the power generated in each of these grids comes from photovoltaic (solar) systems. They differs in two ways (with respect to the topic of this article) from traditional turbine‑driven alternator systems. Firstly, they can almost instantaneously increase their output power (up to the maximum possible at the moment) when needed in the event of loss of capacity elsewhere. That is a positive for such systems.
But they do not have an equivalent of the “inertial energy” held by traditional turbine-driven alternator systems. Thus they cannot briefly “punch above their weight” to cope with the dynamics of loss of another major source—a negative for such systems. Thus the planning of the configuration and management of power grids has be done under a new set of realities.
Issue 1, 2024.04.18. 10 pages, 2661 words. 2 figures. PDF format, 141 kB
The maximum power transfer theorem Recently new; this issue updated
One of the most useful theorems of electrical engineering is the maximum power transfer theorem. It states that if a source of electric energy can be characterized as a fixed voltage (its internal voltage) in series a with fixed resistance (its internal resistance), the greatest power can be extracted from that source by a load whose resistance is equal to that internal resistance of the source.
But it is easy to be misdirected by this theorem and apply it in ways that are incorrect.
This article explains the basis for this theorem, and clarifies why some misguided “applications” of it are erroneous. A “proof” of the theorem, through calculus, is given in an appendix.
The article shows some ways in which the theorem can be practically exploited in AC circuits. It finally discusses the extension of the theorem to the general case of AC operation, where the internal impedance of the source is not purely resistive.
Issue 2, 2024.01.16. 17 pages, 2970 words, 14 figures, 2 appendixes. PDF format, 371 kB.
Power and exponential functions New
Two important classes of functions in mathematics are the power functions and the exponential functions. But the power functions include an exponent, resulting in them often being mis‑described as “exponential” functions. This article (in a not very mathematically rigorous way) clarifies the difference between these two classes of function. Also discussed is the widespread use in the press of “exponential” to mean a rapidly‑increasing increase in some factor.
Issue 1, 2024.04.28. 6 pages, 1222 words, 3 figures. PDF format, 295 kB.
A recreational problem in statistics describes a situation in which an intelligence operative, wishing to know (on very short notice) the fraction of the inhabitants in a certain city who lived north of a river running through the city, contacted one inhabitant at random and determined that he lived on the north side of the river. From that, it was determined that “the best estimate” of the fraction of the inhabitants living north of the river was 2/3. In this article we discuss the possible meanings of that answer and, choosing one for further study, analytically derive that same value.
Issue 1, 2005.12.19. 5 pages, 1385 words. PDF format, 96 kB
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SOLAR (PV) ELECTRICAL ENERGY SYSTEMS
Solar electrical energy generation are increasingly important to the overall scheme of electrical energy provision, whether for electric power utlitlies,. large industrial installations, small business, or individual residences.
The following articles discuss various aspects of this area. Specific details and examples are in terms of North American practice.
Solar energy—quantities, and units
It is today increasingly common for both businesses and residences to install solar electrical energy systems.
This article introduces various quantities involved in the basic physics of solar energy systems, and their units.
Issue 1, 2023.12.24. 2 pages, 519 words. PDF format. 50 kB.
Calculating the position of the sun
In a solar photovoltaic (PV) electrical energy system, the power that can be developed at any instant is approximately proportional to the solar irradiance on the PV panel array. This in turn is the product of the incident solar flux density and the cosine of the angle between the direction of the sun and the normal to the panel surface. At any moment, that angle is a function of the orientation of the panel (the direction in which its normal points) and the direction of the sun (which we can characterize as comprising its elevation above the horizon and its azimuth), with the latitude of the site a parameter.
Thus, in projecting the output of a planned solar photovoltaic system, it is necessary to take into account the angular “travel” of the sun over the site, which in turn requires us to be able to calculate the position of the sun, in terms of its elevation and azimuth, at intervals over the daylight hours of a day, and then over many days (perhaps all the days of a year).
In this article, I give and discuss the equations that, as a close approximation, give the elevation and azimuth of the sun for a given location at a given time in a given date. An appendix gives the equation for calculating the solar declination, a parameter that appears in that equation.
In another appendix, I develop on a geometric basis the equation for the elevation of the sun at solar noon on four special days: the days of the vernal equinox (spring), summer solstice, autumnal equinox (fall), and winter solstice. In a companion appendix, I demonstrate how these results are consistent with the more general equation for the elevation.
Issue 1, 2024.01.06.11 pages, 2658 words, 3 figures, 4 appendixes. PDF format, 160 kB.
Principles of residential solar electrical energy systems Revised
Today it is increasingly common for private residences to be equipped with solar electrical energy generating systems (photovoltaic systems). This article discusses a number of technical matters for such systems.
Considerable attention is given to the matter of the maximum power point (MPP) of a photovoltaic panel, and the schemes and systems used to exploit it. Also discussed is the matter of various architectures of residential solar electrical power systems. The article also discuses the matter of net metering arrangements between the solar system user and the local electrical power utility. Special arrangements for minimizing the risk to technical workers from the high voltages involved in the photovoltaic panel “strings” are also discussed. The roles of production metering and consumption metering in these systems are also discussed.
Several appendixes elaborate on various of the topics involved.Photos illustrating portions of a typical installed system are included.
Issue 11, 2024.01.21, 46 pages, 10,229 words, 30 figures, five appendixes. PDF format, 1.8 MB
Solar PV panels–power output ratings
An important “rating” of a solar photovoltaic (PV) panel is its maximum electrical output power under some stated solar radiation incidence (irradiance). This property may be determined under three common sets of standardized test conditions, and is usually stated by the manufacturer as determined under one or more of those sets of conditions.
The common sets of test conditions are called STC (“standard test conditions”), NCOT (“normal cell operating temperature”, and PTC (“PVUSA test conditions”). This article concisely describes these, and discuses some ramifications of each. Background is given in the important underlying technical concepts.
Issue 1, 2023.12.24. 11 pages, 3046 words. 5 figures, one appendix. PDF format, 463.4 kB.
Solar energy systems—solar panel and inverter power ratings Revised
In a typical solar energy generating installation for a residence with modest electrical energy usage, the photovoltaic panel array might be “rated” at a total output of 6.4 kW, while the inverter, which takes the DC power generated by the panel array and converts it into AC to feed the house load and/or feed back into the power grid, might be rated at a maximum output of only 5.0 kW. This at first seems inconsistent. This article discusses that and related issues.
Issue 3, 2024.01.12 6 pages, 2227 words. 3 figures. PDF format, 134 kB.
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What property does “magnetic field” denote? Revised, one error corrected
When we have at some point the phenomenon we describe, overall, as a “magnetic field”, it has two distinct quantifiable properties.
But we find that often when “magnetic field” is used to identify a specific quantifiable property, sometimes it means one of these two properties and sometimes the other. Over the years this has led to innumerable misunderstandings in technical writings.
In this article, I illuminate that ambiguity and make recommendations for usage to avert any misunderstandings.
Issue 3, 2024.01.23. 8 pages, 1850 words, 2 figures. PDF format, 200 kB.
The Vernier scale in measuring instruments
The Vernier scale is an ingenious construct by which the scale of a direct‑reading mechanical measuring instrument (e.g., caliper, micrometer) can be read with far finer resolution than would otherwise be practical.
Its operation depends on the human visual system’s uncanny ability to discern even a tiny misalignment between two abutting line segments.
This article describes the construct and gives examples of its application to familiar measuring instruments.
Issue 2, 2023.10.08. 11 pages, 2600 words, 13 figures. PDF format, 494 kB.
We have traditionally encountered watthour meters as used to measure the electrical energy we buy from an electric utility company. In modern times, new types of such meters have come into use, and they are often used in new ways. This series of articles covers various matters related to this area.
The calibration constants of an electromechanical watthour meter New
The classical analog AC watthour meter involves a special type of AC motor with an aluminum disk rotor. Its rotational speed is proportional to the amount of power flowing through the meter. The revolutions of the disk are totted up by an elaborate set of gears driving a number of decimal dials, the overall indication of which represents the net number of kilowatthours passing through the meter since its birth.
The relationship between revolutions of the disk and the energy flow that represents is described by two numerical “calibration constants”, Rr and Kh, which are almost always stated on the meter nameplate. They usually have what seem to be very curious values. Those two constants are directly related. If we know how to interpret those, we can determine the power now being consumed by timing the rotation of the disk with a stopwatch.
This article describes the meaning of those two constants and their relationship.
Issue 1, 2024.01.25. 8 pages, 2872 words, 2 figures. PDF format, 151 kB.
Principles of electromechanical watthour meters Recently new, this issue expanded
For many years, the classical electromechanical watthour meter (typically in a glass “fishbowl” housing) was a fixture in every building that was a customer of an electric power utility company. It measures the cumulative energy drawn from the utility’s “power grid” (as we say today) by the user’s loads in the building, so the utility could bill the user appropriately. Today most of these electromechanical watthour meters have been replaced by electronic watthour meters, which afford many benefits to the utility company.
But the principles on which electromechanical watthour meters operate are very ingenious, and fascinating. This article explains those in some detail. Considerable background is given in some matters of physics and electrical engineering that play important roles in the story.
Issue 2, 2024.02.04. 28 pages, 6622 words, 19 figures. PDF format, 1.14 MB
Hall effect devices in electronic watthour meters New
The “Hall effect” is a phenomenon in certain materials (notably semiconductors) where, if a current is passel along the x axis of a “slab” of the material, and a magnetic field (in the sense of a magnetic flux density) is applied along the z axis, a voltage appears across the slab along the y axis. This principle is used, for example, to sense the DC current in a conductor in a “clamp‑on DC ammeter” (by sensing the magnetic field caused by that current in the conductor).
In certain “electronic” watthour meters, a Hall effect device is used not only to sense the current flowing through the conductors through the meter, but within itself to perform the multiplication of instantaneous voltage and current values that underlies the measurement of electrical power (and in turn, of electrical energy).
Issue 1, 2024.02.15. 11 pages, 2948 words. 4 figures. PDF, 247 kB.
Transportation and Agriculture
The Oliver No. 23-B Reversible Sulky Plow
The Oliver no. 23-B reversible sulky plow is a horse‑drawn riding plow that can be set to turn the soil to either side, thus allowing the use of highly-efficient plowing “patterns”. The machine was manufactured by the Oliver Chilled Plow Works of South Bend, Indiana, over the period from about 1917 through 1934. It has a very ingenious mechanism, the crafty geometry of which obscures its principles of operation.
Many authorities consider this machine to represent the pinnacle of design for plows of its type.
In this article I describe the Oliver 23-B and explain its mechanism and the way it supports the many special features of the machine. Some background is first given on the concepts of plowing.
Issue 4, 2013.05.24. 23 pages, 6285 words, 20 figures. PDF format, 1159 kB.
Principles of Steam Locomotive Valve Systems
The familiar kind of steam locomotive is propelled by a reciprocating steam engine. Central to the operation of any such engine is a valve system, which admits steam to the cylinder during certain portions of the cycle and exhausts the cylinder to the atmosphere during other portions.
In a steam locomotive, valve systems that are robust and free from the need for delicate adjustments are desirable and are widely used. They nevertheless follow ingenious principles to approach ideal engine performance over a range of operating conditions.
In this article, we postulate a simple mathematical model which, it will turn out, closely follows the actual operation of most of these valve systems, and we see how it produces a beneficial plan of steam admission and exhaust.
Appendixes then review the actual construction and operation of three widely‑used “valve gear” systems, for two of them showing analytically how they closely fulfill the abstract mathematical relationship between piston and valve movement we assumed in the body of the article, thus closing the circle. Another appendix discusses the matter of power‑assisted reversing mechanisms.
Issue 2, 2019.12.27. 40 pages, 10,750 words, 18 figures. PDF format, 900 kB.
Spring Equalization for Steam Locomotives
The axles of steam locomotives are supported by springs, for the obvious reasons and some less obvious. If the axle ends were each independently sprung, owing to the high stiffness (spring rate) the springs must have, even small local undulations in the height of the rail will cause substantial dynamic variation in the distribution of the locomotive’s weight over the various wheels, with undesirable effect.
To mitigate this problem, locomotive designers soon developed an array of clever mechanisms for equalizing the wheel‑to‑track force over most of the driving wheels on a given side. Because of the special duties of the first set of driving wheels and the preceding unpowered “leading” wheels, there are different objectives there, fulfilled by a more complex mechanism. This article describes the principles of these equalization mechanisms.
Issue 1, 2011.10.17. 18 pages, 4486 words. 16 figures (including 6 photographs). PDF format, 682 kB.
Rail Signal Aspects and Indications
Wayside railway signaling practice in the U.S. is a nightmarish web of operating rules, signal types, aspects, aspect names, and indications, differing between the different roads and even their individual divisions and locations. Much of the “vocabulary” involved is extremely curious and counter-intuitive, a result of the long historical evolution of this field and of the industry.
This article begins with a review of the evolution of the actual “signals” themselves. Then a consistent (if tortured) thread of syntax is identified for the mainstream of current practice, and its principles and most common application are discussed at length. An appendix illustrates, with extensive charts, much of the vocabulary of a hypothetical system with explanatory notes. Other appendixes cover specialized related areas.
Issue 10, 2019.10.20. 68 pages, 15,472 words. 22 figures, 5 appendixes. PDF format, 1.8 MB
The Episcopal Civil War in the Episcopal Diocese of Fort Worth
In the 1990s and early 2000s, The Episcopal Church, the U. S. member of the worldwide Anglican Communion, was embroiled in a controversy—a “civil war”—so virulent as to hold the potential of schism of the denomination, or even of the Anglican Communion itself.
In late 2008, the Bishop, most leaders, many priests, and many individual parish churches of what was then known as the Episcopal Diocese of Fort Worth (covering a large region in North Texas) left The Episcopal Church and affiliated with another Anglican Communion church, and claimed control over the land and buildings of many of those parish churches. The result was a gigantic upheaval in the church lives of Episcopalians in that area. Complex litigation ensued over many issues, even over which organization had the right to use the name “The Episcopal Diocese of Fort Worth”.
This article begins by describing the overall context within which this startling action took place, and continues to describe the various happenings in its immediate aftermath, including the onset of the litigation and its general premises.
The article then takes a ten-plus year hiatus, picking up the story in 2021, when the preponderance of the litigation had come to essentially its final conclusion.
Issue 1, 2021.11.11. 21 pages, 6790 words. 2 figures. PDF format, 232 kB
The Geometry of “Toward Mecca”
Muslims worldwide are exhorted, with regard to their daily formal obligatory prayers, to face in the direction of The Kaaba, a stone structure located within the Sacred Mosque in the city of Makkah (often presented as “Mecca”), Saudi Arabia. It is considered the holiest place in Islam. The concept is often described in the popular press as praying “toward Mecca”, thus the title of this article.
While that mandate seems simple on the surface, when we consider that the Earth is not flat, we immediately run into the matter of how should “in the direction of The Kaaba” be interpreted if one is any significant distance from The Kaaba. Countless works have been written by Islamic scholars over the years on this matter. Two pragmatic premises for making the determination (giving quite different results) have been widely “taught” in modern times by different Islamic advisors. In this article we examine these two premises from a standpoint of the geometry they seem to imply. No attempt is made to judge which is the “most appropriate”, although some personal observations are offered.
Issue 1, 2011.08.13. 12 pages, 3160 words, one figure, one appendix. PDF format, 167 kB
A Modern Automated Machine Quilting System
A quilt is a fabric item, often in the form of a bed covering, with two fabric layers between which is a layer of insulating “batting”. In one style, the three layers are held together by a pattern of continuous stitching, a process known as quilting. This may be efficiently applied by a quilting machine, in which a sewing machine (“sewing head”) travels on a bidirectional carriage system over a portion of the entire quilt. In an automated machine quilting system, the sewing head is driven by a computer‑controlled servo system so as to automatically execute the desired pattern. In this article we describe a modern automated machine quilting system utilizing a newly introduced sewing head and a mature commercially‑available PC‑based computer control system.
Issue 1.1, 2008.10.23. 32 pages, 8500 words. PDF format, 786 kB
Stitch Formation in Rotary Hook Sewing Machines
Most modern general-purpose sewing machines form a lockstitch by way of the rotary hook technique. The working of this system can be quite mystifying, and depends on a clever design worthy of a magician’s kit. In this article, we explain how the rotary hook mechanism produces a lockstitch.
Issue 3, 2008.10.28. 11 pages, 2365 words, numerous illustrations. PDF format, 369 kB
In 2013, the incandescent‑lamp based house lighting system of the Rohovec Theater at New Mexico State University–Alamogordo, in Alamogordo, New Mexico, was completely replaced by an LED based system. As with the earlier system, one of the two sets of lights in the new system—intended for use in connection with theatrical productions—was controlled by the theater’s theatrical light control system, and was intended to be dimmable, using a modern dimming interface system intended for such fixtures. But from the completion of the upgrade, that set of lights could not be dimmed, and in fact on some occasions one half of those lamps flickered. This article tells the story of how this malfunction was diagnosed and corrected. Extensive technical background is provided.
Issue 1, 2016.05.08. 18 pages, 4662 words, 8 illustrations. PDF, 770 kB
Information systems and computers
The ASCII and "ANSI" Character Sets
In connection with personal computer technology we often hear reference to the "ASCII" and "ANSI" character sets. This paper describes what these are and explains the basis of the acronyms used to identify them, including why "ANSI" is an inappropriate designation for the second of them.
Issue 2, 2004.07.18. 4 pages, 1300 words. PDF format, 79 kB
ASCII, Unicode, and in Between
The standard coded character set ASCII was formally standardized in 1963 and, in its “complete” form, in 1967. It is a 7‑bit character set, including 95 graphic characters. As personal computers emerged, they typically had an 8‑bit architecture. To exploit that, they typically came to use character sets that were “8‑bit extensions of ASCII”, providing numerous additional graphic characters. One family of these became common in computers using the MS-DOS operating system. Another similar but distinct family later became common in computers operating with the Windows operating system.
In the late 1980s, a true second‑generation coded character set, called Unicode, was developed, and was standardized in 1991. Its structure provides an ultimate capacity of about a million graphic characters, catering thoroughly to the needs of hundreds of languages and many specialized and parochial uses. Various encoding techniques are used to represent characters from this set in 8‑ and 16‑bit computer environments.
In this article, we will describe and discuss these coded character sets, their development, their status, the relationships between them, and practical implications of their use.
Information is included on the entry, in Windows computer systems, of characters not directly accessible from the keyboard.
Issue 3, 2010.06.15. 19 pages, 5240 words. PDF format, 132 kB.
Early in the unfolding of the modern era of computer science, it was recognized that computer memory modules typically had location sizes that were integral powers of two. To allow sizes of commonly-encountered memory modules to be stated with modest-size integers, it became common to speak of the size of computer memory modules in terms of a multiple unit of 1024 (210) locations. Sadly, rather than adopting a distinct name and symbol for that multiple, the workers just hijacked the prefix term, “kilo”, and symbol, “k”, used in science and engineering (since 1795) for a unit multiple of 1000. This practice then escalated (in a not-always-consistent way) to larger multipliers such as mega (M) and giga (G). The result was ample opportunity for misunderstanding. Now, an international standard provides distinct, unambiguous prefix names and symbols for a series of “binary” multiples.
This article gives historical and technical background in this matter and describes the new (but, sadly, rarely-used) scheme of “binary” multiples.
Issue 1, 2009.02.25. 7 pages, 2400 words. PDF format, 81.3 kB
Microsoft Excel: Number representation, precision, and accuracy Recently new, extensively revised in this issue
It is widely said that in the spreadsheet program Microsoft Excel numbers are represented, and calculations done, to a precision of 15 significant (decimal) digits. That is essentially true, but does not tell the whole story.
It is tempting to expect that the accuracy of calculations and results will be commensurate with that precision. But not necessarily—some times not even close.
The reason is that numbers are actually represented in Excel in a binary floating‑point form, with a precision of 53 bits. While that scheme can precisely represent integers (to a precision of 15 significant decimal digits) over a gigantic range, it cannot always precisely represent numbers with a fractional part, even such a harmless‑seeming one as “1.1”. The consequences may be unexpected (and troublesome) errors when doing calculations in Excel.
Issue 4, 2024.04.28. 14 pages, 3135 words, 3 figures, two appendixes. PDF format, 206 kB.
Image Annotation Objects in Picture Publisher 10
Often when editing images in Picture Publisher 10 we may wish to add annotations, which might consist of circles or squares to call attention to certain features, lines to lead to “callout” text, and so forth. It is desirable that these annotations be objects, so that they can be moved, resized, rotated, otherwise modified, or removed.
There are no provisions in Picture Publisher 10 for directly generating geometric figures as objects. However, there are straightforward, although not trivial, procedures for doing so indirectly.
This article gives the details of several such procedures.
Issue 1, 2011.08.28. 8 pages, 2235 words/ PDF format, 69.0 kB
The names “octatherp” and “octotherp” for the symbol “#”
In the mid 1960’s, the terms “octatherp” and “octotherp” began to be mentioned as names for the symbol “#”, and this practice continued for many years. These terms arose in a very interesting way. This article tells the story, as best it can be reconstructed at this later point in time.
The article also contains, in an appendix, information about the related term "octothorpe".
Issue 3, 2014.12.06. 13 pages, 3940 words, one appendix. PDF format, 84.8 kB
Scientific Notation and Floating Point Representation
Scientific notation is a scheme for presenting numbers over a wide range of values that avoids the consumption of page space and the other inconveniences of long and unprofitable strings of leading or trailing zeros. A related convention provides for the convenient entry of numbers over a wide range into calculators or their introduction as constants into computer programs. A closely‑related concept, floating point representation, provides for the compact representation of numerical values over a wide range inside computers or in data recording structures. In this article we will examine these concepts and then give details (some very tricky) of various standardized conventions for their use. The metrics range and precision are discussed. Background is given on pertinent basic number theory concepts.
Issue 1, 2011.07.20. 19 pages, 4680 words. PDF format, 125 kB
The Ohsen AD1601 is a very handsome but quirky men’s wristwatch with both analog and digital aspects. The analog aspect (quartz crystal controlled) is conventional, with hour, minute, and center seconds hands. The digital aspect uses a small display window to provide for a number of features, including chronograph operation. The size and location of the digital display window makes these features somewhat impractical. The instructions provided by the manufacturer are in Chinese on one side and sort-of English on the other. In addition to being hard to follow, they do not seem to accurately apply to this model. This article describes the watch, and provides (hopefully) clearer instructions for use and setting.
Issue 1, 2019.03.10. 10 pages, 2384 words, 2 figures. PDF format, 231 kB
Doug and Carla - an Urban Legend
Many of my friends and colleagues have expressed interest in how I got together with my wife, the lovely and fabulous Carla. Here's a brief recount of that deal.
Issue 3, 2023.09.01. 2 pages, 1295 words. PDF format, 38 kB
The author received his engineering degree in 1957. In 1970, unknown to the author, a custom, already followed for many years in Canada, was newly introduced into the U.S. A student graduating from engineering school takes an oath to uphold the ethical standards of the engineering profession, and receives a simple stainless steel ring as a symbol of that commitment. Through a fascinating chain of events, the author, in 2016, just a few days after his 80th birthday, received his engineer's ring. This article tells that story.
Issue 1, 2020.09.08. 8 pages, 2378 words, one appendix. PDF format, 74.5 kB
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