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Ultra-Speed
Theater Television Optics
By L. T. SACHTLEBEN and G. L. ALLEE
The general properties of a reflective optical system of the Schmidt type are discussed, with particular reference to practical considerations of design and application in the theater. The relationships of focal length, projection distance and incident screen illumination are illustrated. Also discussed are the factors on which resolving power and fine-detail contrast depend. Some facts relating to the design, material and application of the aspheric or ogee lens are given.
JL HE PROBLEM of satisfactorily projecting a kinescope image upon an external screen has concerned television engineers for many years. Early attempts were made with ordinary projection or photographic lenses of both domestic and European origin. The difficulties were many and serious, and were never completely overcome. One of these was that the face of the kinescope had to be flat or even concave toward the lens, because of the shape of the image surface of the lens. Such shapes are not good from the standpoint of the electron optics of the kinescope, and they are not good mechanically, especially if the tube is large. Added to this was the practical impossibility of getting a lens that would pick up enough light from the kinescope
Presented on October 15, 1951, at the Society's Convention at Hollywood, Calif., by L. T. Sachtleben and G. L. Alice, Advanced Development Engineering, RCA Victor Division, Camden, N.J.
to produce a magnified screen image of adequate brightness and size for theater use. The kinescope image is low in candlepower per unit area compared with the tungsten and arc lamps used in the usual motion picture projectors. As a result, the light from it has to be gathered much more efficiently than in usual projectors. In other words, the projection optics must have much more speed for theater television projection than for motion picture projection from film.
The answer to the need for an ultraspeed system began to take form in the middle 1930's. Donald O. Landis, an optician and designer and maker of telescopes, got the idea that the new high-speed Schmidt astronomical telescope could be used for projection television. This instrument covered a wide field at efficiencies ranging five to ten times greater than the best available lenses. Also, it required the face of the kinescope to have the convex shape
November 1951 Journal of the SMPTE Vol. 57
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