A Stereo/Photo Glossary Page 1 of 34 A STEREO/PHOTO GLOSSARY (Second edition, version 93.5/97.4a) by: Craig Daniels and Dr. Dale E. Hammerschmidt This short work is intended for anyone interested in stereoscopic pursuits, but particularly for those who are trying to create stereoscopic images. We hope that the words and phrases to be found here will become useful tools rather than obstacles in your approach to "3-D" imaging. We stress that this is a compendium of terms that we have found useful, confusing and/or interesting; while we have tried to make it accurate, we do not represent that it is complete or of great scholarly depth. Some entries are long, because we found the subject interesting or we knew a lot about it; some are short for the obvious other reasons! We have tried to keep the tone conversational, rather than strive for uniform and rigid style; we've not felt ourselves above an occasional wise-crack. Additions, corrections and improvements are always welcome --- we see ourselves as editors rather than authors. (Glossary is available via diskette or e-mail.) * ANSI: American National Standards Institute. See next entry. * ASA: (1) American Standards Association. Although the expression "ASA" is still applied to U.S. film speeds, the "American Standards Association" changed its name to the "American National Standards Institute" in 1969. Their standards are referenced by ANSI numbers such as "PH3.11-1953" (which describes the 5p format used in cameras like the Stereo Realist and the Kodak Stereo 35). (2) As a film speed, it now appears in conjunction with the European DIN number (see) in the format "100/21"" which, as such, is the "ISO" speed. Relative film speed is proportional to the ASA value. Absolute film speed is determined by a formula which in turn describes the judgement of a panel of experts who have been shown the results of carefully controlled trial exposures. If you don't like the results of using the prescribed speed, use another and term it your "EI" or "exposure index. Photographers often prefer to use higher EIs for transparency films (to prevent color wash-out) and lower EIs for negative films (to ensure adequate negative density). * Accessory lens(es): Lenses that --as with planar cameras-- enable the stereo camera to focus and/or converge closer (see: "Angle lenses"). Close-up lenses allow close focusing without the complications of excessive lens extension, need for exposure compensation, and the like. Other accessory lenses include those which alter the angle of acceptance, producing in effect modest wide-angle or telephoto effects. * Accidental Stereo Effects: Those stereo effects encountered by --for example-- fusing two postage stamps with printing irregularities or encountering a pair of photographs in which there has been incidental lateral displacement between the two exposures. Sometimes called a "found stereo" by analogy to that venerable genre, the "found poem." * Accommodation: The refocusing of the eyes as their vision shifts from one distance to another. When using a stereoscope or "free-viewing", accommodation is uncoupled from "convergence"; those two processes are normally linked to one another as a reflex. * Achromatic (lens): Lenses designed to avoid chromatic aberration. Simple one- element lenses and prisms, when focusing rays of "white" light can't bring the rays to http://www.uci.net/~goto/glossary/ 03-09-17 A Stereo/Photo Glossary Page 2 of 34 a single point (or image made up of points). Instead, a family of images (a blur) consisting of differently colored versions of the image/point(s) are created. (1)(VL-3) An achromat brings the main colors contained in white light to a common sharp focus. This is achieved by having two or more lens elements, which differ in shape and/or refractive index, such that their chromatic aberrations tend to cancel each other out. For example, a mildly diverging (minifying; minus-diopter) lens of high refractive index may be placed in front of a stronger, converging lens of lower refractive index. The red end of the spectrum will be diverged more (than the blue end) by the first element, but also converged more by the second one --- if the balance has been well chosen, all colors will focus at the same place. * Actual image: An optical image which is "actual" in the sense that it can be shown to exist by putting a screen at its position and seeing it in projection. It is sometimes also called a "real" image. The image in the camera at the film plane is an example. (As distinguished from a virtual (see) or "Space" image.) * Acuity: See: "Stereo acuity. * Aluminum Screen: Usually also with a "lenticular" surface (diamond pleated so as to disperse light back into the audience), the aluminum coating preserves the polarization of the two beams from a stereo projector. A white mat or glass beaded screen won't. For rear projection, simple ground glass or special lenticular glass screens (ie: actually micro-lensed, and for dispersion) can also preserve polarization. * American stereoscope: See: "Holmes". * Anaglyph: A stereogram in which the left and right images are superimposed but printed in complementary colors (often red & blue-green). It is decoded and viewed by placing correspondingly colored filters over the eyes. The most practical form of stereo illustration for the printed page. * Analyzer: See: "Decoder". * Angle lenses: Supplementary lenses for a stereo camera used for close-ups. They both focus and converge the camera's design window to a closer plane. A single large lens covering a pair of camera lenses will serve this purpose. * Aperture: Any optical opening such as a camera iris or that at the back of a camera that masks the film and determines the frame format. * Auto-stereogram (graph): A stereo image that requires no auxiliary device or technique to be viewed (e.g.: Nimslo lenticular prints). * Axis: See: "Photographic axis," "Optical axis," "Visual axis," "World War Two, Major Alliances of. * Bands: Ghost zones seen at the sides of an incorrectly trimmed/masked view. * Base: Usually understood to be the distance between the left and right lenses when a scene is stereographed. In this case, "stereo base" is roughly equivalent to the term "stereo displacement, although that (2)(VL-4) latter term may also be expressed as an angle (see illustration). http://www.uci.net/~goto/glossary/ 03-09-17 A Stereo/Photo Glossary Page 3 of 34 3 b = stereo base; d = distance (film plane to Object b also equals stereo displacement, if camera's optical axes are parallel) (as in most stereo cameras) Stereo displacement may also be expressed in terms of the angle subtended: 2 arctan (b/d); this is common only when rotational displacement has been used in extreme close-up work * Bates, Joseph: The man normally credited with producing the first of the classic American ("parlor") stereoscopes, complete with a hood and an adjustable stage/card holder. * Beam splitter: (1) An optical element that reflects and passes specified percentages of the light rays striking it. For example, a beam-splitting prism is often employed in a microscope to allow viewing of the image through the eyepiece(s) at the same time one is photographing it through a separate upright tube. The old Canon "Pellix" camera used a pellicle-mirror-type beam-splitter instead of a moving mirror, to allow SLR function without mirror "slap"; this technology has recently been improved, and reintroduced in the Canon EOS-RT. (2) A "stereo attachment" (see); technically, most prismatic or mirror stereo attachments are more properly termed image splitters or frame splitters, as they do not split an individual beam into components. The difference in light path between the two devices is illustrated below. * Binocular instrument/viewer: Any 2- lensed viewer, stereoscope, or a device for viewing a planar image with both eyes. * Binocular vision: --implies, but might not refer to stereoscopic vision --which requires the healthy function of a discrete area of the brain which sorts out relative parallax differences between the eyes. See the "Cyclopean", "Stereopsis", and the preceding entries. * Brewster, Sir David: A great man of many accomplishments among which was the invention of the kaleidoscope (1816) and the lensed stereoscope (presented in 1849, and published in 1856 in his The Stereoscope). This he referred to as the "lenticular" stereoscope as opposed to the earlier Wheatstone mirrored (but unlensed) stereoscope (which see). He carefully described the use and collimating nature of off-axis or prismatic lenses, particularly the use of lens segments ("semilenticular" elements) for such purposes. Consequently, all lensed 'scopes can be referred http://www.uci.net/~goto/glossary/ 03-09-17 A Stereo/Photo Glossary Page 4 of 34 to as "Brewster stereoscopes", whether full or semilenticular, but a fully lensed stereoscope (whether or not used off-axis) is frequently referred to as a "Claudet" 'scope. * Camera axis: See: "Photographic axis. * Cancellation: The mutual extinction of the unwanted images (i.e.: no vestigial "left" image should be seen by the right eye) in a stereo viewing system where the presented image is a coded composite of both the left and right components. * Carbutt, John: The first production 35mm camera (the "Homeos") was a stereo camera and stereoscopy preceded photography itself; thus, it is only fitting to note that the innovation and first use of dry plates and celluloid film was in the field work of the pioneering stereographer John Carbutt --not, as commonly believed, by George Eastman and the Kodak labs. (See: John Carbutt in On the Frontiers of Photography by Brey.) "Cardboarding: The characters in hand-drawn stereo cartoons look as though they are cut out of cardboard.