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

the great light-catiierint. power of rca's television projection optical system is demonstrated in a set-up (left), which shows the bright image of the philadelphia skyline, inverted in the center lens, unde- stroyed by full daylight illumina- tion, a phenomenon of the system is a "ghost" image (right), which appears in the air about two feet away when a small object is sus- pended immediately in front of the spherical mirror. the "ghost" in this case is an rca lapel emblem. ..^ mr\ aspherical system, for projectinp television images from cathode-ray tubes onto a viewing screen, was ready; special tubes were built for it, and the first demonstration was given at the Camden laboratory. Research engineers viewing the demonstration were astounded by the brightness of the projected pic- ture but, while the definition of the system seemed nearly satisfactory for the quality of the picture then transmitted, it was not high enough for the pictures planned for the immediate future. Mr. Engstrom then assigned a number of engi- neers to the many problems con- nected with producing aspherical reflective projection systems of high light gathering power, high contrast, and high definition. Two immediate applications seemed ob- vious: first, a theater television system for pictures about 15 by 20 feet, and second, a home television system with pictures around 15 by 20 inches in size. The new engineering group tackled the problem from many angles, theoretical as well as prac- tical, and the results were very gratifying. The first public show- ing of a theater-television system was made by the Radio Corporation of America when it demonstrated at its annual stockholders' meeting in New York City on May 7, 19-10, a projected-television picture 4y2 by (■> feet in size with a high-light brightness well above the 5 foot- lambert value. The demonstration was given before some 300 stock- holders and press representatives. The same system was shown in- formally to members of the FCC on February 5, 1940, in Camden, N. J. The optical system used in these demonstrations had been com- pleted long before the demonstra- tion. Landis applied for his patent (U.S. No. 2,273,801, now granted) in 1938. The next step was to build a sys- tem for a full-size theater screen. This was done and on May 9, 1941 a demonstration of such a system, using a 441-line television signal and a projection screen 15 by 20 feet, was formally given before a large group of invited guests. The demonstration was held in the New Yorker Theater, 254 West 54th Street, New York City. The pro- gram included dramatic sketches from the NBC studios. Lowell Thomas, a singer, and was clima.xed with a championship boxing bout. Previous to the formal May demon- stration, one was held in the same theater on January 24, 1941 for members of the FCC and the press. Among several workers, besides Landis, whose efforts contributed to the improved optical systems used in these demonstrations were I'". G. Ramberg and D. W. Epstein, who worked out the theory of the finite-throw systems and produced practical designs: also, R. Leusch- ner, whose skill in working glass surfaces saved much time and effort. System Highly Efficient In the system demonstrated in New York, a scene transmitted from a studio is reconstructed as a picture on the curved wide end of a cathode-ray tube about 7 inches in diameter. This picture is very brilliant, but small. The spherical mirror, 30 inches in diameter, gath- ers the light emanating from the tube and reflects it through a 22*,'2- inch lens on the theater screen. This screen is the regular motion picture screen. All the light (except for slight losses in reflection and transmission), which the large mir- ror gathered, finds its way to the screen, and this accounts for the superiority of the new optical sys- tem over conventional projection lenses. While a great deal of effort was being devoted to the theater televi- sion, the home-projection television receiver was getting as much atten- tion if not as much publicity. Op- tical systems for home projection were being built, tested, rebuilt, improved and tested again. The same result as with the theater-size equipment was obtained with liv- ing-room-size pictures, namely: a large gain in light with ample reso- lution and contrast. The major obstacle to the use of reflective optical systems in jiro- jcction television receivers for the home has been the high cost of the aspherical lens. The spherical mir- ror while quite large, ten inches in diameter and more, is an old famil- i.ir item to the 150-year-old optical industry, since most of the conven- tional optical surfaces are spherical and are easily made. With the aspherical surface, similar to a figure of revolution of a shallow letter S around one of its ends, the story was different. Such a figure is not a naturally generated surface and there were no machines for the straight forward production of such surfaces. True enough, as- tronomers, with their traditional patience and lack of hurry, man- aged to produce excellent aspherical lenses of such type on machines used for making astronomical in- struments, but only by a tedious step-by-step method. [26 RADIO AGE