Journal of the Society of Motion Picture Engineers (1930-1949)

of the commonly used phrase "Binocular vision," I reasoned that it is possible to use "two eyes" in certain cases, but not to be able to see stereoscopically. For example, the conventional binocular microscope has two oculars, but only one objective; and thus when using such a microscope binocularly, one does not see stereoscopically. This is also true of some binocular viewers for single Kodachrome transparencies; also when viewing any single photograph or painting binocularly the subject matter cannot be seen stereoscopically. Thus it would seem that the only requirement to actually view subject matter stereoscopically is to change the angle of convergence of the eyes for different planes of depth. We view present two-dimensional color motion pictures on the screen with both eyes, or binocularly, but we cannot see the subject matter stereoscopically because of the absence of the requirement to change convergence for different planes of depth. This would be a case where all the factors that Mr. Dudley would like listed could be activated, but we still could not see the subject matter stereoscopically. This is the reason I chose to use "Stereoscopic vision" rather than "Binocular vision" as the sixth factor of depth perception. It seems to me that his reasoning "that stereoscopic vision is the net result of the various contributing factors" is based on a fallacy. Stereoscopic vision is achieved in the "Anti-Aircraft stereoscopic height finder" without any of the contributing factors Mr. Dudley mentions, except the "faculty of convergence." The determination of the slant range of aircraft in this case, depends solely on this factor, and as I chose to say "Stereoscopic vision." In connection with Mr. Dudley's objection to my use of the expression "Optical infinity," and that I indicated that it could be considered as 20 ft, I would like to point out that this is a common expression in the field of ophthalmology and optometry, and to all American trained optometrists the expression immediately suggests 20 ft, since this theory for many years has been and is being taught in American colleges and universities (see textbook Outline of Optometry by I. M. Borish, page 36, Sec. 8 Al, or Physiological Optics by W. D. 7oethout, 4th ed., Pro fessional Press, Inc., Chicago, 1947, page 38, paragraph titled "Principal Foci.") The next paragraph of my paper, contrary to Mr. Dudley's opinion, is based on the fact that there is a direct relationship between accommodation and convergence. Namely, that when converged at a certain distance, the eyes in a normal individual will also automatically focus for that distance and vice versa. This relationship is thoroughly discussed on pages 431 and 432 of A. C. Hardy and F. H. Perrin's The Principles of Optics, first edition, ninth impression, Camera Craft Publishing, San Francisco, 1943. Thus, if what Mr. Dudley says is true it would seem to me that referring to the examples he gives of a film depicting objects moving toward or away from the observer, that the eyes would also want to change convergence. If they change their convergence to follow the apparent position of this moving object, the result would be double imaging. This also should occur "with great rapidity," but I don't believe it does. I maintain, as indicated in my paper, that as long as subject matter in the three-dimensional motion picture appears no closer than 6 or 8 ft from the observer, accommodation errors will not result. I cannot agree with Mr. Dudley on the cause of headaches amongst some older people who go to the movies, since it is common knowledge in ophthalmic practice that they lose their power of accommodation as a result of progressive hardening of the crystalline lens as they grow older. This would indicate to me that as long as they were wearing glasses corrected for the screen distance, the subject matter on the screen would remain always in focus. Therefore it is interesting to note that when this be the case, especially with three-dimensional motion pictures, they will see subject matter clearly even when required to converge on three-dimensional screen objects, which could conceivably appear as close as two or three feet in front of their faces. As an added prediction, they will quickly realize that for such a phenomenon, they will not need to "peer" through their "bifocals." I prefer not to disclose as yet what improvements have been made in connection with the alternate frame system. However, I would like to assure Mr. Dudley that the 73