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

DEVELOPMENT MODEL OF LARGE-SCREEN TELEVISION PROJECTOR SUSPENDED FROM rHEATKR BAIAONV. PICTIRKS AS LARCE AS 18 X 2-1 FEET HAVE BEEN PROJECTED WITH THIS APPARATUS. Large-Screen Television Two Basic Methods of Projcctinv:, Thcatcr-Sizcd Images Notf Undergohig Series of Praclical Tests By Ralph V. Little. Jr.. Engineering Products Ocpt., liCA Victor Division LAKGK-siTeeii television systems J for theaters and auditoriums have been developed in two forms, both of which are underjfoinK a series of practical tests. One is the direct projection system by which hiRh-brilliance kinescope imaK^s are projected throuffh an efficient re- flective optical system; the other, an intermediate film system usinK' standard motion iiicture projection techni(|ue. after the television im- ages have been photoKi'aphed on motion picture film and suitably processed. The direct projection television system consists of three major ele- ments. One is the projection kine- scope which is the source of the lipht image, the second is the optical system which projects the image onto the screen, and the third is the .screen from which the final image is viewed. The kinescope used in the direct system is similar to the direct view- ing tube used in the conventional television receiver, except that pro- jection kinescopes have a much greater light output due to higher voltage operation, for which they are spitially designed. The elements of the optical sys- tem consist of a spherical mirror, n correction lens, and a projection kinescope tube. The lenses now used in large projection systems are made of plastic, formed in glass moulds by a cold-setting process. Lenses as large as twenty inches in diameter have been made by this process. Reflective optics have been adapted for large screen projection up to 18 by 24 feet. The largest system ever built consisted of a 42-inch mirror, a 26-inch lens and projection kinescopes of either 12- or 15-inch diameter, operating at 80,000 volts. The high cost of the 42-inch mirror system has indicated the advisability of concentrating on smaller optics and increasing the voltage capabilities of the seven- inch projection kinescope in order to make a compromise system which would be successful commercially. Three Units in Intermediate Plan The alternate system of large screen television projection is the intermediate film method which consists of three major units. The first is the television recording unit with a qualit.>» television monitor and a special 35mm motion picture camera: the second consists of a high-speed processing machine, and the third, the conventional .'?5mm theater film projector. Such a sys- tem can be so integrated that the time elapsing between the appear- ance of the image on the kinescope and its projection on the viewing screen is less than one minute. A special camera was devised which would compensate for the difference between the 30 complete images per second as used in tele- vision and the standardized rate of travel of motion picture film at 24 frames per second. This camera al.so provides for sound-on-film re- cording. In this camera a precision shutter is required to give the proper ex- posure to the film. In terms of the television .system, the exposure must be accurate to less than one-half of a scanning line or one part in .30,000. Improper exposure shows up as a black or white band when the wrong number of television lines is re- (Continucd on page SO) [26 RADIO AGE]