British Kinematography (1953)

November, 1953 SPOTTISWOODE \ CURRENT 2-D AND 3-D TRENDS 135 admits that he does not think his system capable of practical realization at present. Putting these solutions aside, there are therefore only trick solutions of the kind which at present do not exist. I will give you an example of what I mean. An inventor believed in what he called " altermittent " vision, i.e., that the eyes see left and right alternately. His idea was that if only the frequency of this k' altermittance " could be found, and the two pictures projected accordingly, a perfect separation of the two images would be provided. I think that the idea is crazy, but it illustrates my point of a factor of human vision not yet lighted upon, but which has the means of selection other than by a complex lenticular type of screen. So little is still known fundamentally about human vision, especially binocular vision, that it is conceivable that such a discovery might be made. B. Honri : Has the author any observations on the Ivanoff system ? The Author : The Ivanoff system which was, in effect, a practical realization of the idea of a Belgian, de Noaillon, works within its limits, but these limits are too restrictive to provide satisfactory commercial screening. It seems, from the geometry of the system, that the selection cannot be very good, and that the number of seats in the cinema must be drastically reduced. Probably the most crippling defect is that the audience has to sit in one plane and that the projection beam has to be in the same plane as the audiences" eyes. All of this is discussed in Gabor's patents — one stage of his reasoning defines the de Noaillon-Ivanoff conditions and shows why they would not be practical in the commercial cinema. But I must give the Russian credit for making this idea work at all. W. S. Bland : If the Vectograph system is adopted there will have to be increased illumination on one film. What effect will the resultant heat have on this film ? The Author : It should be said that Vectographic film is approximately J 2 more effective than the double-band version. But it is quite true that there is one arc instead of two, so the heat problem is quite serious. In large drive-in theatres in the U.S.A., where the current rating is as high as 175 amps., forced air and water are used to cool the film down. It is very possible that the very thin base now being introduced by DuPont will buckle less, because it will have more radiating surface for its volume. B. S. Chadwick : What tolerance should be allowed in the matching of lenses for projectors ? The Author : They should, in principle, be as accurate as the camera lenses, which we try to match to ±0-25 per cent. In that respect I think you are completely in the hands of the manufacturers. F. G. Gunn : What observations had the speaker on curved screens ? The Author : A curved screen tends, when it is of the high reflectance type, to make the reflectance more uniform to a person sitting at the side of the cinema. Also the focal plane of projector lenses is noticeably concave, and therefore, by curving the screen out slightly, the definition at the edges is improved. But when the curve is carried to excess, as in Cinerama, for the sake of engulfing the audience, the distortions are severe. Only because the whole effect is so impressive do audiences tend to overlook these distortions. W. S. Bland : I was very interested to hear the suggestion for the use of a frame three perforations in height, using the Vectograph system, because if the left and right eye images were printed on one film with a suitable separation for the two optical systems, with a frame height of three perforations and running at 16 frames per second, the film speed would be 90 feet per minute. This would mean that the present recording apparatus could be utilized for making the necessary sound tracks. The Author : That is an idea we had in mind about a year ago. However, we felt with Vectograph coming along it was unnecessary to devise ways in which the two images could be put one above the other or side by side on film. The new magnetic materials being introduced for The Robe have a very high coercivity and will give a signal/noise ratio approximately 15-20 db higher than the best that can be achieved to-day. R. L. Hoult : I understand that CinemaScope, with four magnetic recording channels, will necessitate a change in the standard perforation. What is the American reaction ? The Author : I discussed this point two weeks ago with an American technician, who said that the new sprockets would only necessitate a relatively small and inexpensive change in projectors. When asked whether the new prints, on account of their smaller perforations, would have a shorter life, he said that probably they would, but that the life of prints was not determined by print wear, either of perforations or by scratching, but generally by the obsolescence of the films themselves. With the new perforations, wear tests have shown that films would run 500-600 times through the projectors with reasonable care. When asked whether any picture unsteadiness would be caused by projecting film with old fashioned larger perforations on the new sprocket, the technician said that tests had shown that adequate picture steadiness could be achieved. When, in England, I asked one of the laboratory chiefs for his views, I was told that there was much anxiety about getting the film through the developing and printing machines when it had different perforations. The cost of equipment conversion would also be a difficult problem. A Member : What causes eyestrain ? The Author : We were discussing this the other day with the Medical Research Council, who I hope are going to do some experiments, because the reasons