The motion picture projectionist (Nov 1930-Oct 1931)

March, 1931 Motion Picture Projectionist 21 Some Aspects of Stereoscopic Projection (Continued from page 19) degrees from the other. Analyzing devices, properly adjusted to match the polarizing planes of the projected pictures, exclude the "L" picture from the right eye and vice versa. Since the polarization is largely broken ur. after reflection from the usual diffusing screen, the method requires a metallic screen, or one giving specular reflection. This system may be characterized as of scientific rather than practical interest. (6) Separation by alternate "L" and "R" projection and viewing. This idea is quite old. The validity of the method of blinking the eyes synchronously with the projected pictures was demonstrated by shifting peep holes in extensions on the side of a double projecting lantern having a rotating shutter before the lenses. The two views appear on the screen to be superposed, but one is cut off before the other appears. Persistence of vision was thus relied on to give a continuous impression in a projected picture years before the film motion pictures were developed. One of the early writers suggested electrical blinkers in front of the eyes, worked from contacts on the projector shutter mechanism. More than twenty years ago, the writer constructed and demonstrated privately a stereo-projection system in which the 60-cycle house lighting service was used to maintain synchronism between the alternate "L" and "R" screen pictures and a portable electric lorgnette. This shutter device, on a cord long enough to permit viewing (while observing the picture as seen in relief on the screen) was used at various distances and angles. Actually, a side view of a screen gives no more distortion for a true stereoscopic picture in relief than it does for a single flat picture. However, while moving about, some of the effects obtained were quite unexpected. The autochrome process came onto the market at about the time of the stereo-projection development cited, and afforded means for showing stereo pictures in color by projection on the screen. The Public's Reaction In spite of the realistic and striking effects possible, it has always seemed questionable as to how the public would react toward stereoscopic motion pictures requiring a special viewing device for each observer. This question can be best answered only by trial, although this involves special development all along the line, viz., cameras, printers, projectors, and viewers. Can a stereoscopic effect be obtained without two pictures and a separating device? In the opinion of the writer, the only proper answer is, "No." The illusion of reality in a picture may rest upon many things, none of which may properly be called stereoscopic. For example, perspective, relative size, shadows, color, progressive haziness, motion, etc., all aid in estimating distance in a single picture. But none of these meet the true stereoscopic test, which is seeing with one eye something which is hidden from the other. DISCUSSION Mr. Palmer: I have heard statements made that when viewing stereoscopic pictures in which the pictures are separated optically, there are certain people who are color blind with respect to viewing the picture in this way. I wonder if in Mr. Taylor's investigation of the subject he has found this to be the case. Again, is the stereoscopic effect enhanced by viewing the picture from the focal point; that is, the point where the negative image was at the time the picture was made? Mr. Taylor: I have never found that anyone having two normal eyes would have difficulty in seeing the picture in the box form if the lenses were focused. As to viewing angle, if we should want to make a stereoscopic picture and see it as it appears in nature, the proper relation between the focal length of the taking lenses and the distance from which the finished stereogram is viewed, must be maintained. I have taken a picture outof-doors and mounted it; then, looking at the view with one eye and at the picture with the other eye, it was possible to have the picture register almost exactly with the scene itself. Sometimes it is desirable to exaggerate the stereoscopic effect. The eyes of a man are a certain distance apart. The eyes of a cow or horse are farther apart. If we should want to see as an animal sees, we should have to adjust this distance to suit. This procedure is followed by astronomers where they make a separation of 186,000,000 miles, taking the picture first from one side of the ecliptic, and six months later from the other side. On very distanct objects the two lenses may be separated by a yard or two. This gives a relief effect with mountains which is exaggerated, but which may be desirable in stereoscopic surveys. "Favoring" One Eye Mr. Edwards : Don't you think the reason why some people cannot see stereoscopically is that they get into the habit of favoring one eye, and they really use only one eye. Sometimes, with a single, flat picture taken with a single lens we can obtain a stereoscopic effect. Why can we not obtain that effect in a motion picture? We know that the illusion can be created by having a stationary foreground and a moving background. Mr. Taylor: Some people look into a microscope and do not see any thing because they do not know what points to focus on. That is to some extent a matter of training. This can be overcome with a little training. As to the statement that single pictures show the stereoscopic effect, I have never seen them, although many factors in motion pictures contribute to the illusion of reality. Sometimes one may think that nothing is lacking and say the effect is stereoscopic, but this seems a misuse of the term. Mr. Morrall: Some time ago I took some pictures of a room in which a man was working with material which covered him with dust. The lighting was the same as they used in a preceding scene, where the dust was not present. When projected, I was amazed to see a stereoscopic effect in the picture. This might be attributed to the fact that the coating of dust reflected light in such a way that it caused the stereoscopic effect. "Back-Lighting" Process Mr. Ross: I agree with Mr. Edwards that in motion pictures we frequently do find stereoscopic effects. The effect is produced on the West Coast by what is known as "backlighting." Experiments show that back-lighting produces this illusion whereas without back-lighting the illusion is not present. Mr. Taylor: I have already stated that many things, such as light and shade, relative size, and motion help to estimate distance, but it will be unfortunate if we confuse the two ideas. Effect of Eye-Strain Mr. Fritts: On viewing a normal scene, the eyes are focused at a definite point and the rest of our vision is strained, in the sense that the eye is trying to accommodate its vision to all visible planes. It has been suggested that this may have something to do with the appreciation of depth. In certain experiments which we have made, a picture having a marked foreground and distance was viewed through a large uncorrected lens. The eye, under those conditions, is subject to eye-strain on the borders, which is akin to the eyestrain of normal vision, giving the effect of depth. Is this correct? Mr. Taylor: Without the actual set-up, I can only conjecture. This may be a case of factors other than stereoscopic, which aid in judging distance. ' Mr. Phelps: When looking at a contact paper print and then at a lantern slide of the same negative, projected on a well-illuminated screen, my eye seems to tell me that there is more depth in the projected image than in the paper print. Mr. Taylor: Perhaps because the lantern slide more closely approximates the proper light and dark ratios. In real life, we have a large ratio, and in a good slide we can more closely approximate this. No print has natural ratios. In the case of transparencies we. come nearer to the proper values. W. E. Nears 5,000 Mark Western Electric sound system installations in the United States now total 4,902.