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1947-48 Theatre Catalog, 6th Edition, Page 584 (566)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 584
Page 584

1947-48 Theatre Catalog, 6th Edition, Page 584

THE NECK OF THE TELEVISION TUBE is inserted in the conJike tube at the front of the projector us is being done here. While the projector is designed for fixed focus operation, the various controls mounted on the unit permit the operator to adjust the brightness, locus, and framing of the picture. Once the equipment is set for the start of a program, only slight adjustments will be needed later.

tem developed and incorporated in the advanced experimental large-screen television projector, the quality of screen illumination provided is said to be comparable with a conventional f/2.0 projection lens, while the amount of light reaching the screen is about six or seven times as great.

The 6-by-8 Project-or

Let us, then, look to what the equipment practicalities are, as of this present moment in the light of the Atlantic City demonstrations, which was put on for late-staying delegates to the first annual convention of the National Broadcasting Company and the early-arriving delegates to the sessions of the National Association of Broadcasters. Cooperating in the demonstrations were the American Broadcasting Company, Inc., Philco Corporation, NBC, and RCA.

The optical system of the projector consists of two elements: (1) a 21-inch spherical mirror and (2) a 14-inch aspherical correcting lensemounted in a tubular housing. A 7-inch, metal-backed, high-intensity developmental projection tube is placed in such a position that its face is directed toward the magnifying spherical mirror that is pointed at the projection screen. The large spherical reflector greatly magnifies the picture picked up from the face of the projection tube and projects it through the 14-inch aspherical lens onto the beaded screen 15 feet away.

The use of a spherical redective lens with a large aperture introduces difficulties in focusing and results in a certain amount of distortion. For this reason the specially ground, weak, aspherical correcting lens is used to introduce an amount of distortion which is equal to and opposite that caused by the spherical mirror. The effect of the aspherical lens, then, is to balance out the distor

tion of the reflective lens, and the rays of light arriving at the screen produce an undistorted and greatly enlarged version of the original picture, which, in this case, is 8 feet wide by 6 feet high, or producing an enlargement of about 16 diameters.

The special projection tube, or kinescope, employed in the large-screen projector was especially developed for use in reflective optical systems. Into this projection tube was designed a metalbacked screen such as is used in all RCA projection tubes. In order to obtain light of proper brilliance for projection, extremely high acceleration voltage is required, in this case 50,000 volts.

Tube engineers developed new types of phosphor compounds which were coated with a fine metallic film, thin enough to allow the passage of electrons. This greatly increased the tube brilliance. In addition to this, a new type of electron gun and other elements were developed to withstand the very high current used by the projector. The result is a tube which produces a brilliant white light, nearly as dazzling to the eye as that from an arc lamp.

The developmental tube, the refiective optical system, and the necessary power supplies and control equipment are all self-contained in one unit. While the projector is designed for fixed-focus operation, the various operating controls which are mounted on the unit permit the operator to adjust the brightness, focus, and framing of the picture. Only a slight adjustment is necessary for an entire program.

A new type of power supply has been incorporated into the large-screen projector which eliminates the danger usually present when high voltages are used. A high-frequency oscillator power supply is used, instead of the conventional GO-cycle type, which preventswthe stor age of high voltage in the filter circuits, and, thus, eliminates the potential hazard to operating personnels. '

Television signals can be fed to the large-screen projector from any regular television source, such as network coaxial lines, microwave television relay sources, from studio or camera pickup sources, or any other standard RMA video signal sources.

The lG-by-24 Proiec'l'or

The investigations that led to the development of equipment for projecting a 6-by-8-foot picture did not stop at that point, but, rather, continued toward tibigger and better" ends-that of pictures really of theatre size. That Was to have been expected-but to have the announcement by the Radio Corporation of Americas Ralph V. Little, Jr., and I. G. Maloff of an experimental model television projector for an 18-by-24-foot pictures come just 41 days after the earlier demonstration was surprising in its suddenness.

The new equipment, which more than doubles the screen size developed by British engineers, operates on the same principle as that already described. Here the optical system employs a spherical mirror 42 inches in diameter, an aspherical correcting lens 36 inches in diameter, and a high-voltage kinescope with a screen surface 15 inches in diameter. The kinescope is designed to operate at 80,000 volts.

As experimentally designed and tested ea public demonstration has not been made at the time this material was prepared-the large projector has a 40foot throw.

When this equipment is perfected for actual theatre use-and the concurrent matters of program material and when, and how, to use it are reasonably settled-the question of its location will have to be solved.

With theatres having balconies, whose rail is not more than 40 feet from the screen, the positioning of the television projection equipment seems to be easily solved-even if at the expense of a few seats. And it is not possible to think that, as still further refinements are made, the equipment may yet be installed in the projection booth itself. When this time comes, it may be necessary to provide projection rooms with an over-all width of about 32 feet, or about twice what the ideal booth for two projectors is presently considered to be.

Since the desire to utilize television is not dependent on the presence of a balcony, provisions for equipment must be found for the shelf-IeSS theatres. At present the logical thought is directed toward suspending the projection equipment on a pulley arrangement, lowering it when needed. As a variation of this idea, and perhaps a more satisfactory solution, would be to suspend the equipment from the ceiling girderseassuming, of course, the original construction would sustain the added loadein a permanent and accurately positioned installation. The location would be such that the cinematic projection beam would just clear the lower end of the television housing.

Such installation in non-balcony situations presupposes are further development: that of remote control. Such

1947-48 Theatre Catalog, 6th Edition, Page 584