International projectionist (Jan-Dec 1957)

Television and Motion Pictures By ALLAN LYTEL Continuing this series, the author discusses certain problems that are still plaguing the TV industry in the matter of translating motion pictures to a tube. PART II THE PROBLEM of projection television has been approached from many angles. Two successful projection tubes have held out considerable promise. One is a bent-neck tube. An electron gun is mounted in its neck, so arranged that this gun will sweep a cell which acts as the tube screen. The cell contains many very fine flakes of graphite suspended in a liquid medium and is made of transparent material to allow passage of light. With no potential applied to this cell, the individual graphite flakes will have a random motion which obscures all of the light, hence there is no picture projected upon the screen by the lens. When a potential is applied across this cell the graphite flakes will line up so they are at right angles to its face. Graphite Flakes Motion Since the individual particles are thin flakes, light will pass whenever they are at right angles to the face of the cell. Where a slight difference in potential exists between the two faces of the cell at any one point, some of the graphite flakes will be at right angles to the face of the cell but others will be in random motion. Thus this point of slight potential will correspond to gray on the viewing screen. When the individual flakes of graphite have no applied potential, they move about in the liquid and no light can pass through the cell. The electron beam is so arranged that it sweeps across the tube screen, which is one of the faces of the graphite cell. This cell itself must be made of a material which is not only transparent but also insulating. A transparent cell is needed in order that light may pass through ; the insulating property is important in order that the various points of the cell at different potentials may not affect one another by leakage. In fundamental optical principle, though certainly not electrically, this tube resembles the Skiatron in that the electron beam controls the passage of light. Where the Skiatron gave a dark trace image, this tube gives a light trace image. That is, this tube will allow light to pass wherever the electron beam causes a difference in potential between the cell faces. Relay Projection The same general principle of on outside light source projected through a television tube has been used in yet another type of development. A bent neck cathode ray tube has a crystal plate mountedinside the tube. This plate has a transparent conducting coating on its rear face and a fine mesh metal screen mounted in front. Light is passed through this tube screen from an outside source, after which it is collected by a projector lens and thrown upon a viewing screen. The -Condensed by permission from Chapter 6 of Mr. Lytel's book: "TV Picture Projection and Enlargement," John F. Rider Publisher, Inc. Oscar F. Neu Dies Oscar F. Neu, owner and president of Neumade Products Corp., manufacturers of equipment for motion pictures, radio and TV, died at his home in Crestwood, N. Y. on August 26. He was 71. Neu had always been active in motion picture industry affairs. He was cofounder of Theatre Equipment and Supply Manufacturers Association, and served as its president from 1946 to 1951. In 1955 he was elected President Emeritus, the only member of that organization to be so honored. In a long and varied career in the theatre, motion picture, and TV industries, Neu was at times a merchandiser, a vaudeville performer, a screen actor and director, a broker of motion-picture by-products, and finally a manufacturer and distributor. He was a member of the Motion Picture Pioneers and Variety Clubs International, a fellow and governor of SMPTE, and a 32nd degree Mason. crystal is a material like zincblende, an insulator that can develop points of varying potential on its surface due to secondary emmission. This secondary emission is caused by the electrons coming from the gun mounted in the neck of the tube. As electrons from the gun arrive at the crystal, they cause secondary emission because of their high speed. The secondary electrons pass to the fine mesh screen, leaving the crystal with points having differences in potential. The number of electrons knocked from the crystal screen depends upon the video information which varies the intensity of the electron base. Thus the crystal plate has a fluctuating difference in potential between its front face an drear coating, and there are many individual spots on the screen that have different potentials with respect to the rear coating. This condition may be compared to that on the Iconoscope mosaic, which produces a similar effect although through an entirely different mechanism. This crystal screen produces no visible picture image whatsoever. Polarizing Action When two polarizing plates, A and B, are so mounted that their axes are at right angles no light passes through such a system. Light may go from the original source through screen A and through the crystal plate, but this light is stopped by polaroid screen B. However, a potential difference between the front and back surfaces of the crystal screen has a remarkable effect on the light. If light traveling from screen A to screen B passes through a charged area of the crystal screen its polarization will be so rotated that some light can pass through polaroid screen B. Thus when this screen has no potential difference applied at all — that is, when there is no video information supplied and no electron beam is present — no light will be passed through to the projection (Continued on page 30) INTERNATIONAL PROJECTIONIST SEPTEMBER 1957 19