Robert L. Mclntyre
There’s a type of picture arrangement that appears quite often in landscapes submitted in club contests and the exhibitions, but you rarely see it in the slides that are accepted by the judges. It’s easy to describe by likening it to a layer cake. There may be a strip of sky across the top of the picture, a layer of distant shoreline below it, an area of water in the middle, and some land in the near foreground. Most of the lineé in such a picture are horizontal. This is particularly unfortunate in stereo because horizontal lines alone are incapable of producing any stereoscopic depth effect.
Vertical lines give the strongest threedimensional effect. When they are placed at different distances we have to exercise convergence in order to bring together their dual images. Horizontal lines are weakest in 3D. Since all the stereoscopic displacement is sidewise, they overlap themselves in the two stereo images.
This provides a good stereoscopic reason for avoiding layer-cake landscapes, just to reinforce the basic pictorial argument that they don’t make interesting pictures. Often a change in camera position will make it possible to introduce strong vertical or diagonal lines that will make your picture more effective.
Commercial photographers, wedding photographers, and amateurs with experience in using more flexible camera equipment have long been awaiting accessory lenses for stereo cameras. Up to now there have been only supplementary lenses for use in stereo close-ups, but Realist, Inc., has just announced a wideangle attachment for general use. It consists of a pair of matched lens assemblies mounted in a holder designed to lock on the front of the camera. These lenses are made so that they produce a 25-mm focal length when used in conjunction with the regular camera lenses. They do it without affecting either the regular aperture settings or focusing scale. A special viewfinder is a part of the wide-angle attachment, which fits all Realist cameras prior to the new ST45 and is priced at $119.50.
The shift from 35-mm to 25-mm focal length means an increase of about 40 percent in the area that the camera covers. Putting it another way, the horizontal angle of view is increased from the usual 36.5° to 49.5°. That’s a wider field than you get with regular 35-mm cameras, in spite of the extra width of their pictures. The Leica with normal 50-mm lens, for example, takes in 42°.
Wide-angle stereo is a very practical solution to many problems the commercial photographer encounters. When he has to shoot a big piece of machinery in a small room, he often faces the difficulty of not being able to back away far enough to get all of his subject into a single picture. The wide-angle attachment will prove of real value under con-
ditions like these. It helps you to wor closer to your subject and still cover wide area. Pictorial applications of th device are more difficult to predict.
The stereoscopic ideal, theoretically, [ the “orthostereo” condition in which th focal length of camera and viewer lense is the same. If you have 35-mm earner lenses and 35-mm viewer lenses, whe; you look at a slide you will see the sam thing you would have seen if your heai had been located at the camera positio: in the original scene. It has become cu; tomary to provide viewer lenses that ar somewhat longer in focal length than th
camera lenses, both because they ar cheaper to make and assemble and be cause they serve to exaggerate the dept] effect slightly in a way that most peopl find pleasing. Today’s viewers run fror 44 mm to 50 mm in focal length. Fe\ people complain, and only the perfection ist is likely to see the difference.
Shortening the focal length of th camera lenses from 35 mm to 25 mir while using the same viewer, might be ex pected to disrupt the ortho-stereo condi tion violently. The change is not as drasti as it would seem. When nothing is closi to the camera, you aren’t likely to notio any difference at all—particularly if yoi don’t have comparative slides of the sanr subject. People look normal at distance over 8 or 10 feet. Occasionally there wil be an appearance of distortion you cai find when you look for it. What happen is that an object at a given distance—sa; 6 feet—continues to appear to be at tha distance according to the stereoscopii depth clues provided by the slide. Yet it image is smaller on the film than yoi would expect it to be at that distance, anc objects within the view display more vio lent perspective than seems normal wher you analyze it. We could interpret sucl pictures as close-ups of miniature subject; or as shots taken at normal distance o: unusual objects which are elongated. AÍ this, however, is interesting in theory bu' of little significance in practice. When wc look at pictures of familiar objects, w( know how they are supposed to appeal and we are quick to discard any visua] clues that fail to confirm this preconceived notion.—fcs