Radio age research, manufacturing, communications, broadcasting, television (1941)

LARGER TELEVISION IMAGES RCA Scientists Solve Difficult Optica/ Problems in Projection — Develop Methods of Moldinii Plastic Lenses for Both Home and Theater Keceiuers. By I. G. Maloff RCA Victor Division, Camden, N. J. IMAGE size in television—for either the theater or the home —is no longer a serious problem in engineering or economics. It is possible to build, as was demonstrated experimentally by RCA just prior to the United States' entrance into the war, pro- jection-type television receivers that reproduce images of any de- sired size up to full theater-screen dimensions. Not generally known, however, is the story of how certain features of one of the great instruments of astronomy — the Schmidt-Kellner camera—were adapted to television projection. The story concerns be- hind-the-scenes laboratory work, calling first for the solution of an unusually difficult mathematical problem in optical design, and finally, for development of a method to reduce the production cycle of a new lens from months to minutes. To those who have seen the all- electronic system of television in operation, it is well-known that images received from a television transmitter are reproduced on the broad, nearly-flat end of a tube called the kinescope. The kinescope can be built in various sizes, but when it is given a diameter much larger than 12 inches the cabinet in which it and its accompanying equipment are housed becomes un- desirably bulky for practical home use. For this reason, it was apparent some years ago that if larger televi- sion images were to be available in homes, a system of optical projec- tion must be developed. Tests with standard projection optics produced screen images that were much too dim for practical use. Thus, the situation called for a new approach —an original conception. It had been known for a long time that aspherical* lenses in com- bination with either spherical or aspherical mirrors may be arranged into optical systems of high defini- tion combined with great light gathering power. Astronomers were first in making use of this principle, especially in an arrange- ment consisting of one spherical mirror and one aspherical lens. The high costs and difficulties in con- structing aspherical lenses retarded more general utilization of such svstcms. Conceives Nen' System Quite a few years ago. D. O. Lan- dis, an optician working in the laboratories of the RCA Manufac- turing Company (now RCA Victor Division), and having contact with the needs and aims of men working on television research, conceived the idea that an optical system could be built using aspherical ele- ments for projection of television images. He realized, too, that the shape of the aspherical lens in his new system would be different from that of the astronomical lens. This, he understood, was because the as- tronomical camera is focused on infinity but in his case a short and finite distance separated the optical system from the projection screen. Landis submitted his idea to E. W. Engstrom, now Research Director of the RCA Laboratories R. LEUSCHNER TESTS AN ASPHERICAL LENS (ABOVE) FOR DEVIATIONS FROM THEORETICAL DESIGN; THE AUTHOR RE- MOVES A PLASTIC ASPHERICAL LENS (BELOW) FROM THE MOLD IN WHICH IT WAS MADE. * Conventional lens design makes use of entirely spherical surfaces; in aspherical lens design, the surface has a variable curvature. (then heading the Research Divi- sion of RCA Manufacturing Com- pany at Camden, New Jersey) and was encouraged to construct a working model. It may be men- tioned here that Mr. Engstrom's action was not in accord with the more conservative opinions of some members of his stafi" at the time Landis commenced his work. The design of aspherical infinite focus systems seemed to oflFer little assist- ance to the evolution of aspherical finite focus projection systems. Landis went ahead struggling with his system and doing most of the work in the basement of his home, where he had a well equipped optical shop. He was then a well known figure among amateur as- tronomers as well as among ama- teur telescope makers. After a few months of long hours at the grind- ing and polishing machines his first [RADIO AGE 25]