Exhibitors Herald and Moving Picture World (Apr-Jun 1930)

28 Better Theatres Section April 12, 1930 the current to the grid, rotates synchronously with the scanning disc, or signal light, at the transmitting end. In other words the screen or grid is much like an electric sign where a shoe contacts various lamps in a predetermined pattern, the pattern in this case following the designation of the signal light at the transmitting station, and building up, as it “sees” them, the features of the subject. As I said before, enlargement and clarification of the image received from one of the two obstacles now in the way of the commercialization of television. Enlargement possibly will be obtained by building larger grids. Clarification, or an increase of light, may be achieved by using an electro-magnetic field to vary neon illumination. This is something entirely new and is one of the next steps in television, according to Dr. William Hoyt Peck, electrical wizard and inventor of the “colorcraft” process. The other obstacle, simplification of apparatus, can only be overcome by constant work at detailed refinement. And that takes time. To consider clarification, even in a very simple way, it is necessary to go more into detail about transmission. In transmission the object to be transmitted has light played upon it by what is called a scanning disc. This is a disc with holes around it which spiral in towards the center. Behind the disc is a light source. In front of the disc is an aperture. In front of the aperture is placed the subject. The disc revolves and the light passes through each hole of the disc successively and plays upon the subject. The effect of this, if done slowly, would be to cover the object with little dots of light in parallel lines, something like the surface of a halftone engraving. One light follows another so quickly, however, that by the persistency of vision the subject appears to be completely illuminated. The reflection of each beam as it illuminates a minute portion of the subject, is picked up by photoelectric cells, amplified and transmitted to the receiving station, where it is reproduced. As holes of the disc pass across the aperture, they illuminate, in rotation, every aspect of the subject. If the disc has 50 holes and is moving quickly, it will produce 50,000 light signals a second, or “scan” subject completely 18 times a second. A.T the receiving end, the apparatus is picking up 50,000 impressions a second in synchronization with the scanning disc at the transmitting station. It must be remembered that each one of the impressions covers only one of the 2,500 contacts on the grid, and while the persistency of vision may tell one that he is looking at a picture which is not very clear, he is actually seeing only one-2, 500th of it at a time. Suppose you watch it for a second. You see 50,000 individual dots take form and die: it isn’t like the cinema, where you are presented with a complete picture which changes 24 times a second. Here you are presented with only a fractional portion of the picture, even if the complete thing should come and go 18 times a second. Now, suppose that all the impressions were maintained till other ones came to Making “television movies.” Players broadcasting a dramatic sketch from the studio of the General Electric Company’s laboratories at Schenectady, N. Y. [PHOTO BY HEWS BUBEAU. GENERAL ELECTRIC] wipe them out. That would give you 2,500 impressions constantly, the first only disappearing when the 2,501st took its place, the second yielding only to the 2,502d, and so on, through the length and breadth of the grid, which corresponds to a screen. Then the difficulty of light, the problem of clarification would be gone. There would be good projection and one of the major problems of television would be solved. That is one of the things being sought by television engineers today. In theory, as it is pointed out, the only thing that is necessary is a large, electrically magnetized steel plate which will lie behind the grid. It is hoped that this magnetic field will maintain the electrical impulses in the neon tube until they are wiped out by another series, and so keep a picture on the grid. In color television today, the same light sources, driving motors, scanning discs, synchronizing systems, and the same type of circuit and method of amplification are used, as in the monochromatic system discussed above. The only new features are the type and arrangement of the photoelectric cells at the sending end, and the type and ar rangement of the neon and argon lamps at the receiving end. New cells, using sodium instead of potassium, have been developed. Their active surfaces are sensitized by a complicated process using sulphor vapor and oxygen, instead of by customary glow discharge of hydrogen. Their response to color, instead of stopping in the blue-green region, goes all the way to deep red. Three sets of cells are used in place of the one set now employed. Each has a gelatine color filter: one of orange-red, another of yellow-green, and a third of greenish-blue. Three series of television signals, one for each set of cells, are generated, instead of one, and three channels are used. In considering the simplification and refinement of the other apparatus now in use, let us begin by examining its limitations. First, there is the simplest method of television, that of still photography transmission, which is much in vogue with newspapers. The American T e 1 ephone and Telegraph Company’s still photography transmission now takes seven minutes for a 5x7-inch picture. The picture is divided into the equivalent of 10,000 elements to the square inch, or a total of 350,000 elements. This requires a transmission of a frequency band of 400 cycles a second on each side of the carrier frequency. And if you plan to transmit images of the same fineness of grain as that which is now sent in seven minutes, you would have to send your complete image in a one-sixteenth of a second and would need a transmission frequency range 7,000 times as great. Three million cycles would be the approximate width of the frequency band. Bearing in mind that wire circuits are not ordinarily designed to carry frequencies of over 40,000 a second, and that with radio systems, uniform transmission of wide signal bands becomes extremely difficult, you can understand at once that an image of considerably less detail than the one just considered is imperative, or else some means must be found for splitting up the image so that it may be sent through a larger number of channels. Practical television, from individual to individual, a service to parallel that of telephony is fairly close at hand, according to Professor H. E. Ives, who is attached to the technical staff of the Bell Laboratories. Professor Ives, however, thinks that television will always be much more expensive than telephony ( Continued on page 154)