From Photo-3d

• 5
  • 5P - sometimes known as Realist Format

• 7
  • 7P - sometimes known as European Format

• D
  • Di Marzio Equation

• R
  • Retinal rivalry

• S
  • Stereo window
  • Stereo window violation

From Herbert McKay

These definitions come from Herbert C. McKay's book (see Bibliography). This book is now in the public domain.

American stereoscope.—The common parlor or Holmes version of the Brewster stereoscope. Also Mexican stereoscope.

Anaglyph.—A stereogram of two superimposed images in which the images are blocked to their respective eyes, so each eye sees only its own proper image. The original form was the bichrome in which the images are printed in two complementary colors and viewed through correspondingly colored filters. A half century ago the process of using polarized light instead of color was patented, and today is favored over the color type for projection. In motion picture work, alternate frames are dyed in complementary color and the film run at double speed to produce the alternate anaglyph. Both bichrome and polarized types are now in use. Books and magazines, for practical reasons, are usually illustrated in bichrome anaglyphs.

Anaglyphic restoration.—Reconverting an anaglyph to its original form of two separate photographs to be viewed in a conventional stereoscope.

Autostereo plate.—An obsolete plate with a parallax grid on the back, used for making direct parallax stereograms. Reversal processing.

Autotransposer.—Either a printing frame or machine in which provision is made for transposition by simply pulling two levers.

Auxiliaries, stereo visual.—factors in stereo vision which enhance the stereo relief but which are not essential to stereo vision. The two most important are the effects of perspective and overlapping of distant objects by those nearer.

Base.—The stereo base is the distance between homologous optical points, usually the optical axes of the camera, but also applied to the separation of viewer lenses and at times to human interpupillary.

Box stereoscope.—A stereoscope in the form of an enclosed box as contrasted with the skeleton form of Holmes. Standard in Europe.

Brewster, Sir David.—Probably the true inventor of stereoscopic reproduction, although the claims of Wheatstone are also favored by some. Brewster was the first to point out the overwhelming importance of the subjective in stereo. He also invented the prismatic stereoscope (semi-lenticular) which is properly known by his name, but often called Holmes, Mexican, American and the like. These are only one type of Brewster construction.

Chain stereoscope.—A cabinet stereoscope with the views hung in chains which pass over twin sprockets thus bringing into view one stereogram after another. More familiar in Europe than here.

Chromatic perspective.—See Stereo-chromatism.

Chromatic relief.—See Stereo-chromatism.

Color perspective—See Stereo-chromatism.

Complementary stereoscope.—A stereoscope matched to the camera as is essential in orthostereoscopy.

Compressor, image.—A cylindrical lens used in making stereo motion pictures to permit a rectangular screen image instead of the narrow vertical format of a half frame.

Contour reversal.—A type of space control in which certain elements of the scene are shown in pseudoscopic relief while others are shown in proper stereoscopic relief, although both elements are combined in a single stereogram.

Convergence.—The meeting of visual (or other optical) axes when produced from two separate stations to a common object. Absolute convergence is the actual angle between the convergent axes and is identical with the parallactic angle. Relative convergence is the convergence upon one object within a scene compared with that upon another object. Relative convergence is the more important in stereo photography. Convergence is often said to be the primary stereo stimulus, but this has been disproved.

Convergence camera.—A method of making stereograms by altering the direction of the camera between exposures so the object is centered in both films. Impractical for any subject except one limited largely to one plane. Otherwise more or less serious distortion is introduced.

Conversion filter.—A specific type of color control filter designed to permit the use of artificial light film by daylight or vice versa.

Deviation calculator.—Dial calculator for determination of the range of deviation in any scene before photographing.

Diagnostic stereo.— The use of stereograms to aid in the diagnosis of visual disorders. Diopter.—Ophthalmic lenses (and viewer lenses) are designated by power rather than focal length. The power in diopters is equal to 100 divided by the focal length in cm. Thus a 20 cm lens is five diopter, a 10cm is ten diopter, a 5cm is 20 diopter and so on.

Diplopia (Double vision).—Ordinarily an abnormal visual condition, but normal to all stereo vision outside the macular area.

Drawing, stereo.—A drawing made in duplicate but with stereo differentiation so that when viewed stereoscopically it will have stereo relief. Equivalent distance.—In stereomiorography, a photograph made at a very short distance is viewed as if it were at some greater arbitrary distance, usually "reading" distance. This apparent distance is the equivalent distance. Also applied to other distortions, deliberate and accidental, of stereo relief.

False stereogram.—(See Spreader, Twister, Infusible.) A true stereo pair so mounted that viewing is uncomfortable or impossible.

Flicker projection.—Stereo projection in which the two images are projected upon a screen in rapid alternation, and viewed through a shutter which alternately obscures the right and left eyes in synchronism with the projector.

Frame masking.— Masking the top and bottom of the aperture in a motion picture camera (less commonly in the projector), to produce the desired square stereo screen format.

Free vision.—Any system which permits a true stereoscopic effect to be seen without the use of any kind of viewer.

Fusion.—The visual registration of the two images in the eyes. This is distinct from the phenomenon of subjective synthesis to which the term is often applied. Purely a physioneurological factor.

Ghost image.—Any visual or photographic image which permits objects behind it to be seen; a transparent image. The condition common to images of objects not the subject of direct vision.

Glyphoscope (Trade name).—A simple device now obsolete, used as both camera and viewer.

Grid stereo.—Narrow strip elements from two images alternate. Viewed through a grid spaced before the print, the two eyes see different images due to angular vision through the grid. The least satisfactory of the general integrated type of free vision stereogram.

Guildmount.—A special, rigid, cardboard stereo mount made for the Stereo Guild.

Homologue.—That which exactly corresponds in position, proportion or structure. In stereo applied to corresponding points or parts in the two images.

Homologous distance.—The distance between two homologous points. Identical with base or separation when the homologous points lie at infinity.

Homologous points.—The two point images in the stereo pair which exactly correspond. The two images of the same nail-head in a board, for example, are practically homologous points.

Hyperstereo.—Stereo with an extended base. Results in theoretical error which is practically imperceptible. Reduces apparent distance of objects, which appear as scale models of the larger object.

Hypostereo.—Stereo with diminished base. Used for close-up and stereomicrography.

Iloca.—Stereo version of the 35mm Iloca camera.

Infusible stereogram.—A stereogram so made or so mounted that it cannot be fused.

Integrated stereogram.—A free vision stereogram of the basic grid type but operating upon different optical principles to provide stereo vision from integrated elements of the two images. A lenticular (spherical or cylindrical) screen replaces the grid. Peristereoscopy.

Interocular— Basically the distance between the two eyes; also applied to the separation of camera or viewer lenses. May be variable.

Inversion— The complete reversal of position exhibited in the stereo negative as compared with the true positions. The optical phenomenon which makes necessary the transposition of stereo prints.

Kelvin meter.—Color temperature meter. See Color meter.

Lens, stereo-prismatic.—Supplementary lenses for stereo close-ups which combine both the positive refraction of the conventional close-up lens and a prismatic deviation which permits the image of the close-up object to be centered in the film area.

Light control.—See Color control,

Macular vision.—That part of vision which is characterized by maximum definition and resolution. Also known as "sharp" vision. The object of macular vision is that object upon which the visual attention is fixed.

Magnification of viewer.—In orthostereo the magnification is unity, as the taking and viewing lenses compensate. A viewer with lenses of less than the camera focal length results in undesirable magnification of the image. Magnification as a primary function of the viewer may be ignored when the viewer is a complementary one.

Metastereoscopy.—Reproduction of original in normal proportions but in abnormal size. Common in stereomicrography.

Mexican stereoscope.—Holmes stereoscope.

Mirror stereoscope.—A stereoscope which involves reflection from a mirror. The Wheatstone stereoscope largely used in X-ray work is one type. See Reflecting stereoscope.

Monocular viewer.—This is not a stereoscope. It is a single lens which is used to give to a single photograph a three-dimensional but not stereoscopic appearance. Pantoscope.

Normal stereoscope.—Any stereoscope which uses stereograms whose infinity-homologous distance is substantially equal to the average interpupillary separation, i.e. 65mm. Contrasted with the Brewster in which the I-H points are much farther apart than the normal human eyes.

Orthostereoscopy.—That type of stereo-scopy in which the image is reproduced in full natural size as seen at full natural distance and in full normal degree of relief. Not possible with projection nor free vision; only when an individual viewer is used, and this must be complementary to the camera.

Panortho-stereoscopy.—The nearest approach to perfection in stereo. This is an orthostereogram in which full advantage has been taken of the auxiliaries (q.v.), and which is in full, corrected, natural color. By all means the most perfect type of photograph yet produced.

Parallactic distortion.—A degree of parallax too small or too great for the object size. Objects appear as thin (i.e., silhouettes) or elongated in the direction of the optic axes.

Parallax.—A difference. Specifically the difference of the visual images which result from the two eyes having different points of view. The fundamental external stimulus of stereoscopic vision.

• Absolute P.—The parallax of a given point as determined by the angle between the visual axes meeting at that point.

• Circular P.—Stereo relief produced by rotating the object rather than by having two separate points of view.

• Differential P.—The variation between the parallax of two points upon the surface of an object. The fundamental external stimulus which enables us to see roundness or spatial difference.

• Dynamic P.—The ever changing parallax involved when the eyes shift from object to object. The specific external stimulus of stereoscopic vision.

• Illumination P.—In stereomicrography the production of parallax by opposed light beams rather than by physical difference.

• Relative P.—The parallax of one object or point as compared with that of another. Closely similar to differential parallax but used as a basis of measurement.

• Rotary P.—See Circular parallax.

• Stereo P.—Parallax as specifically related to stereo vision and in contrast to strictly geometric parallax.

Parallax stereogram.— Commonly but incorrectly used to designate an integrated stereogram. Because parallax is the vital factor in stereoscopy, any stereogram of any type might properly be called a "parallax" stereogram. A free vision stereogram, see Grid stereo.

Parallel vision— The normal condition of vision at complete rest. In stereo the ability to fuse a stereogram of conventional type without the use of a viewer. Accomplished by separating the habitual co-action of convergence and accommodation.

Parastereo.—A stereogram which is apparently ortho in quality but which can be demonstrated to possess the anomalous spatial relationship of the stereo telescopic field. To all intents and purposes an orthostereogram of telephotographic type.

PePax.—Coined term to indicate the relationship between the apparent size and the apparent relief of any object. Normal PePax is characteristic of the

orthostereo-gram. Abnormal PePax indicates parallactic distortion.

Perspective.—The disposition of lines to represent a solid object upon a plane surface. In stereo regarded as the complement of parallax. Perspective has to do with "size-in-width" while parallax has to do with "size-in-depth."

Planar— Restricted to a single plane. Ordinary photography in contrast to stereography,

Polarized light.—Light which vibrates substantially in a single plane. Used in stereo largely because of its property of extinguishing an image when planes of polarization are crossed.

Polaroid (Trade name).—A synthetic material which has the property of polarizing light. Used in stereo projection of polar anaglyphs.

Prismatic stereoscope—A stereoscope in which the lenses are really half lenses, thus forming spherical prisms. The Brewster type of stereoscope. Also a reflecting stereoscope using prisms. Often an autotransposing viewer.

Prism diopter.—The unit used in measuring the amount by which a beam of light is deviated by passing through a prism. One prism diopter deviates one unit in 100.

Projection gage.—A film gauge to facilitate mounting stereo films with the correct separation to compensate for various ranges of deviation.

Pseudoscopic.—The effect of untransposed stereo images. Depth values are reversed with far objects seen nearby and vice versa.

Pseudostereoscopic.—A "stereogram" made up of two identical images. As there is no parallax, no stereo relief is seen. Such pseudostereograms have actually been marketed as stereograms.

Separation.—Stereo parallax results from the existence of two optical (visual) stations. The distance between these is the separation. Normal ocular separation is assumed to be 65mm, but in fact varies widely through several millimeters upon each side.

Slide.—Common name for the stereogram.

S. commercial— Stereograms made for sale to the general public rather than for private use.

Sliding base.—A camera base, usually tripod head, which enables a conventional camera to be moved laterally 65mm so that stereo negatives may be obtained by successive exposure.

Space control.—A method of stereography in which objects can be given an apparent position in space which is not the natural one. A miniature human figure for example can be posed upon a tabletop with every appearance of realism.

Spreader.—A stereogram with unit images too far apart necessitating divergence of the optic axes, painful at best and impossible for most.

Stereo.—Abbreviation for stereoscopic, also as prefix for many compound words.

• S. book.—A book illustrated by stereo-grams.

• S. calisthenics.—Exercises for the eye muscles obtained through viewing special stereograms. Intended to inroduce visual comfort and skill rather than to relieve definite visual malfunctions.

• S. chromatism.—The extrinsic depth factor provided by the alteration of chroma and saturation of color with distance. Of vital importance in reproducing stereo depth.

• S. copier.—A special support for the stereo camera in making copies of other stereograms and in photography of small objects.

• S. diplopia.—The diplopia or double image vision normal to all objects outside the macular field, in stereoscopic vision,

• S. drawing.—See Drawing.

• Stereogram—The "picture" used in stereoscopy. Two images either separate, side-by-side, superimposed or integrated.

• Stereogrammetry.—A specialized form of stereoscopy used for making stereograms which are used as a basis for measurement rather than for visual examination.

• S. Guild.—An international association of stereographers which circulates collections of 35mm stereograms among members.

• S. infinity.—That distance beyond which stereo relief can no longer be distinguished. Highly variable. As little as 50 yards for some individuals and as much as 11/2 miles for others. Normal average 670 meters or roughly three-eighths mile.

• S. macro bench.—See S. copier.

• S. macrography.—The stereoscopic photography of small objects at magnifications of —5 to -f 10 magnification.

• S. micrography.—The stereoscopic photography of small objects at magnifications in excess of ten diameters.

• S. microscope.—A compound microscope, usually of the Greenough type which gives a stereoscopic field.

• S. mount.—A physical support for the stereo pair. Usually cardboard in the case of paper prints. Of cardboard, plastic, metal or glass or combinations of these materials for the 35mm films.

• S. prism.—(A). The free vision stereo-prism is a stereo novelty in the form of a cubical solid in which a stereo image is seen. Improved by HCM through introduction of distributed critical angle. (B). A stereo reflector or element thereof, using prisms instead of mirrors.

• S. projector.—A projector used for projecting stereograms upon a screen in such a manner that they may be viewed in relief.

• S. radiogram.—An X-ray stereogram.

• S. relief.—The appearance of solidity, roundness and space seen in the stereo-gram.

• S. Society.—An international (British) organization of amateur stereographers which circulates collections of stereo-grams among members, primarily of the 3x6-inch paper type.

• S. synthesis.—The subjective process by which the stereo image is built up from the two dissimilar planar images transmitted to the visual centers from the two eyes.

• S. Tach (Trade name). —A device to produce stereograms with an ordinary camera.

• S. telephotography.— Telephoto stereoscopic photography. Applied loosely to any stereogram made with long focus lenses, but can be correctly applied only to parastereograms.

• S. telescope—An instrument invented by Helmholtz which provides a magnification of relief rather than the magnification of size common to the conventional telescope. The Battery Commander's binocular (scissors type) combines the double telescope and the stereo telescope.

• S. therapeutics.—The treatment of visual disorders by stereoscopic methods. In wider sense it includes stereo calisthenics and diagnostic stereoscopy.

• S. typogram.—An artificial stereogram produced by differential spacing of printer's type, notably ornaments.

Stereography.—In this field, identical with stereoscopic photography.

Stereomatics.—The art of planning and exposing a series of stereograms in such a way that they will tell a coherent story. The planning of a series of stereograms of definitely related interest and in definite sequence.

Stereopsis.—Stereoscopic vision. The ability to perceive depth visually, and specifically the degree to which such perception is possessed.

Stereopticon.—This word is included to point out the fact that it has absolutely no relationship of any kind with any phase of stereoscopy although it is commonly used when "stereoscope" is meant. Actually, a stereopticon is a dissolving lantern slide projector as used for projecting song slides in the old nickelodeon days.

Stereoscope.—A device or instrument used for viewing stereograms. Not ordinarily applied to the colored or polarizing filters used with anaglyphic stereograms.

• American S.—The Holmes (or Mexican) open type of viewer.
• Bates S.—Bates took over the very crude Holmes skeleton viewer and produced what was substantially the same parlor viewer which we know today.
• Box S.—The enclosed type of viewer. European type.
• Brewster S.—A viewer incorporating two half lenses which thus form spherical prisms, mounted base out.
• Cabinet S.—A stereoscope built as a piece of furniture; a finished cabinet enclosing the automatic or semi-automatic mechanism.
• Holmes S.—Open type Brewster viewer, also American or Mexican.
• Mattey S.—The firm of Mattey of Paris is one of the few which makes viewers exclusively in all grades from folding cardboard viewers to the finest inlaid wood models of automatic classifiers.
• Mirror S.—Usually the Wheatstone or Pulfrich type of viewer.
• Pedestal S.—An automatic cabinet viewer placed upon a cabinet pillar or pedestal which forms a cabinet for the slide collection. Either one or two piece.
• Pocket S.—Folding stereoscope for carrying in the pocket. Usually of inferior quality.
• Pulfrich S.—A small viewer of the Wheat-stone type for tabletop use. See Ryker.
• Reflecting S.—A viewer of (A) the general Wheatstone type or (B) an auto-transposing viewer.
• Ryker S.—A tabletop stereoscope of the general Wheatstone-Pulfrich type but equipped with magnifiers for the study of detail. Military-aerial instrument. One of the best examples of the Wheat-stone type.
• Transposing S.—A viewer which by an arrangement of reflectors or a refracting system makes it possible to view stereo images which have not been transposed. Used with film-strip stereo views.
• 3D S.—This is actually a "viewer" rather than a "stereoscope" inasmuch as it consists of a pair of goggles equipped with polarizing lenses. Used to view stereo projected pictures. Vectographs and the like.
• Universal S.—(A) A viewer which may be used either as a normal or as a Brewster instrument. (B) A viewer, such as a classifier, which will take a variety of sizes of stereogram.
• Wheatstone S.—A viewer which uses separate stereo units, usually facing each other, which are viewed as reflected images. Largely used for stereo X-ray and large print stereo.

Stereoscopic— Having to do with stereoscopy.

• S. balance.—A term used in stereo composition in differentiation from the pictorial balance of a plane surface.

• S. camera.—A camera used for making stereoscopic negatives or images, specifically a dual chamber camera.

• S. vision.—Normal, binocular human vision in stereoscopic. Many beginners seem to think that "stereoscopic" applies only to stereo reproduction. Stereoscopic vision is normal, everyday vision enjoyed by most of us.

Subjective.—In stereo, the final step of stereo perception, the consciousness of the image, the actual step of -'seeing" as opposed to the purely physical, physiological and neurological steps.

• S. anomaly.—The failure of subjective interpretation to conform to stereo theory. Two identical prints (pseudostereo-scopic) mounted as a stereogram when viewed in the stereoscope should appear as images of gigantic size located at infinity. In fact there is no such appearance at all. There is no depth of any kind or degree visible. There are many such effects which can be predicted but which rarely are experienced as a part of the subjective interpretation.

• S. stereo.—That part of stereoscopy which has to do with the interpretation of stereo synthesis; the actual "seeing" as contrasted with geometric and physiological stereoscopy.

3-D.— Popular abbreviation for Three Dimensional. Also polarizing goggles made for viewing projected stereograms and Vectographs. Three dimensional.—Having an appearance of depth or solidity, but not necessarily of stereoscopic quality. Monocular viewers give a three dimensional but not a stereoscopic appearance.

Telestereoscope.—This is a viewer which resembles a pair of opera glasses and is used for the examination of large size stereo pairs, (aerial, X-ray and the like) or stereo pairs projected side by side. Fusion is accomplished through the use of rocking prisms.

Twister.—A stereogram so mounted that the eyes are strained in trying to view it.

Unit magnification.— The principle which states that any photograph should be viewed from a distance equal to the focal length of the taking lens. When extended to stereo this principle becomes that of orthostereoscopy.

Vectograph.—A stereogram made by placing polarizing images upon both sides of an optically active base. Viewed with polarizing goggles.

Viewer.-See Stereoscope.

• Aanaglyphic V.—(A) A mask or goggles containing two differently colored lenses or filters for viewing bichrome anaglyphs. (B) A similar device containing polarizing filters set at 90 degrees to each other for viewing polar anaglyphs.

• Flicker V.—A hand held shutter for viewing flicker projected images.

Window — In a stereoscope the stereogram appears as if seen through a window. The "window" which may be a mask or simply the way the unit prints are trimmed, may be placed in any desired plane; but it is usually placed nearer the observer than any other unit of the picture.