Journal of the Society of Motion Picture and Television Engineers (1950-1954)

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tube, as typified by the iconoscope, (2) pulse-exposure and (3) intermittent film motion, would have to be abandoned entirely and replaced by the new, diametrically opposite concepts of (1) nonstorage (flying-spot) scanning tube, (2) continuous exposure and (3) continuous film motion combined with optical compensation. This in turn would mean that the direction of the light-path would be completely reversed. The important implication of this change is that triplication of the scanning tube would become quite unnecessary for color operation. This would entirely avoid the triple registration problem previously referred to, and would represent a tremendous simplification. Such a system would provide the ideal in television film reproduction. The Solution In attempting to translate these fresh concepts into practice, Philco was in the fortunate position of being able to draw on a rich experience in nonstorage (flying-spot) scanning techniques, as exemplified by its "Flying-Spot Scanner" for opaque and transparent slides, already in use in numerous laboratories and television stations. The practical realization of the remaining two features of the "ideal" system, namely continuous exposure and continuous film motion, were dependent on discovering a suitable optical compensator. This, then, proves to be the key to the whole system. Much time, effort, and money had been spent over the past fifty years by organizations, both here and abroad, to develop such a device but without much practical success. Previous optical compensators were all too inefficient, too complicated or optically imperfect in operation. It is actually not too obvious that the same optical compensating device which is required for the projection of continuously moving film onto a screen is precisely the same device which is required in order to project a television raster from a flying-spot scanning tube onto a continuously moving film. The following explanation may help to clarify these two relationships. In the first mentioned case the function of the optical compensator is to immobilize the film on the screen, whereas in the second case the function of the same optical compensator is to chase the film with an image of the raster. Thus we find in comparing projection of continuously moving film with flyingspot scanning of continuously moving film that the same optical system is used in both cases, except that the directions of the light-paths are reversed and the concept of immobilization is also reversed and becomes "chasing." Technical literature abounds with hundreds of schemes for optical compensation, most of which, incidentally, do not work. Generally speaking, optical compensators fall under three general headings: (1) rotating and/or oscillating mirror devices; (2) rotating lens devices; and (3) rotating prism devices. Mirror Methods. The classical example of a mirror type of optical compensator is represented by the Mechau projector which was designed and built in Germany in the 1920's. It is important because it was the first technically successful continuous projector the world had ever seen. In spite of their relatively large size and complexity many hundreds of these projectors were built and sold, and until very recently their performance was not surpassed by any other similar device. Those of us who are working today in the field of optical compensation in relation to television cannot but have the greatest respect for the genius of Emil Mechau who is now revealed to us as being one of those rare men who in his technical conceptions was literally decades ahead of his time. Great credit must also go to F. Schroter who in the 46 January 1954 Journal of the SMPTE Vol. 62