The Hyper-view Large Format Stereo Viewer
by David M. Lee
Stereo photographers can use a number of different methods to present their images to an audience. The most commonly used methods include projection of 35mm slides on a silver screen, viewing 35mm slides with a lenticular viewer, and viewing of 3½" x 7" stereo cards using a Holmes viewer. While all 3 methods can produce satisfactory three-dimensional effects overall, they are less than optimal in presenting images for which sharpness, detail, or subtle print quality is important. The limitations of the common viewing methods are due to (1) the inherently small size of the 35mm slide, (2) ghosting and other problems inherent in stereo projection, (3) the use of imperfect lenses in lenticular viewers which degrade the image, (4) the use of enlarging papers for stereo cards which are noticeably less sharp under magnification than film, and (5) the lack of freedom to vary the viewing distance in lenticular viewers which, for the most part, results in viewing the image from farther back than the proper viewing distance (in stereo photography this is known as ortho-stereoscopic). [See the box below for an explanation of the proper viewing distance.]
The viewing public for stereo photography has become used to the constraints of seeing stereo images through slide projection and the use of lenticular viewers. Because they have never had the experience of viewing high quality stereo prints using any other method, the mass audience for stereo photography is unaware of other possibilities. Slide show audiences are also generally interested in a different photographic experience and aesthetic--the group viewing of multiple images in a fairly rapid "slide-show" sequence, rather than the leisurely viewing of individual images to appreciate their nuances and subtleties.
The author, who has had extensive experience making and viewing two dimensional "fine photographic prints" from large format (4" x 5" and larger) negatives prior to making stereo photographs, hopes to assist stereo audiences to become more discriminating and more demanding by developing and promoting improved methods for viewing stereo photographs. During the ten years I have been involved in stereo photography, I have constantly searched for improved viewing methods that will enable the viewer to (1) have the image be as sharp as is photographically possible; (2) see the entire image from the proper viewing distance; and (3) scan the image in a seamless fashion, moving closer to examine the details of the print and backing up to take in a wider view.
Convenience and lack of expense were not criteria in this search. My search has led me to develop prototypes for a variety of devices, some of which were too unwieldy and too labor intensive to produce for a commercial market. However, the latest design--which I have called "The Large Format Stereo Viewer"--meets the design criteria described above, as well as being affordable and relatively portable
In the case of the Hyper-View Large Format Stereo Viewer, "large format" refers to the size of the photographic images, rather than the size of the negative. The image size in this case is approximately 10" square. The current version of the Large Format Stereo Viewer is designed for viewing pairs of photographic prints. Future versions will be designed for viewing large format transparencies and stereo panoramas. What the Hyper-View viewing device does is to widen the effective separation of the viewer's eyes from about 2½ inches to about 11 inches. The two prints (or transparencies) are viewed by means of four mirrors, two for each image. The mirrors closest to the prints face them at 45° angles. The other two mirrors are parallel to the first mirrors (right in front of the eyes) and are about half the size of the first mirrors. The mirrors are silvered on the front to eliminate the ghost image that would result from the use of regular rear-silvered mirrors.
The greatest advantage of this over regular lenticular viewers is that there are no lenses in the viewing system to distort the image. In addition, the absence of lenses means that the viewer is not limited to a single viewing distance but can scan details of the image from close up or view the entire image from farther away. The principles used in this viewer are not new. Both aerial stereo viewers and X-ray stereo viewers are similar in concept. The difference between the Hyper-View Large Format Stereo Viewer and the other 2 mentioned is that the others cannot cover a very large field of view. Our viewer covers a 10" square image from an eye position of 15" (the ortho-stereoscopic position for an image made with a normal lens).
While this viewer suits my needs very well, I must add that it is not for everyone. The biggest problem for the average stereo photographer is that a large stereo pair must be made and mounted for viewing. One of the main uses for which I envision it is for gallery exhibitions of my own stereo prints. I am also interested in encouraging other "fine art" photographers who have never seriously considered stereo photography to begin producing creative work in this medium.
The proper viewing distance is determined by multiplying the magnification of the print times the focal length of the taking lens. For example, if the print is 10" high and was made from a 1" high negative, the magnification would be 10 times. If the focal length of the taking lens was 1½", then the proper viewing distance is 10 x 1½" = 15". If the eye of the person viewing the print is 15" from the print then the person will see the scene with exactly the same perspective as if they were viewing the actual scene from the camera position. If the person is closer or farther than 15" from the print then the perspective will be somewhat distorted depending on how far from this position the person is. This distortion is not necessarily a problem, but in the case of stereo photography it would be nice to at least have the possibility of viewing from this position.