International projectionist (Jan 1941-Dec 1942)

is filled with waves of compressed or rarified liquid (perfectly transparent liquid). The frequency or spacing of these waves represents the scanning frequency; the intensity of compression or rarifaction reproduces the intensity of each pulse in the scanning signal, and therefore the intensity of illumination at one point in the original image. The number of wave-crests between the windows of "E" at any given moment is equivalent to the number of points in one-half line of the image. In other words, the image is reproduced, not one point at a time, but one-half line, or 294 points, at a time. Since the liquid is water-clear, it does not of course block light, whether compressed into high frequency waves or not. But it refracts light. Every transparent medium has an index of refraction, which depends on the nature and density of the medium. The liquid in "E," when set into vibration, presents points of high density (maximum compression) and of low density (maximum rarifaction). Where the televised signal is strong, the difference in refraction from point to point along the liquid, will be great; where the televised signal (and therefore the original illumination) is weak, the difference in refraction in "E" will be slight. The Optical Train Space limitations prohibit a full dis» cussion of the optical details of the system. The drawings are intended only to convey the outline idea of the method used. The light source, "A" in the drawing, is a standard projection arc. For the Rialto a hi-low type was selected. It operates at 110-125 amperes. Since current conversion equipment available in the projection room was only 50/50 amperes in capacity, a d.c. line was run in for the television arc. The trim uses 11 x %" standard high-intensity carbons for both positive and negative, and one trim lasts long enough for any program at present contemplated, eliminating any need for changeover. Since there is no film to be changed, there is currently no need for more than one television projector. "B" is a converging lens, the slit "C" and the cylindrical lens "D" cooperate to bar out stray light and to admit only the direct light from the crater to "E." "H" is a septum or barrier. It intercepts or blocks out direct, unrefracted light coming from the lamphouse. When there are no waves in the liquid of "E." no light gets past "H." Everything beyond— to the right of — "H" remains dark permanently. "F" and "G" converge upon the center bar of "H" all the direct (unrefracted) light there is. However, light which has been re fracted by the waves in "E" does not come to quite the same focus, and does get past "H." Such light focuses on the mirrors of "I," which is a mirror-sided wheel, or mirror polygon, and which revolves. Returning again to "E," the standing waves in "E" move across the window opening as one line after another is scanned. If they were projected to a screen they would drift across the screen as a series of waves of light. This effect is counteracted by the carefully synchronized rotation of "I" in the opposite direction, producing the precise scanning effect desired. That is, "I," in combination with the drift of waves through "E," provides the necessary horizontal scanning, a half-line at a time rather than a point at a time. Vertical scanning is effected by "K," another mirror polygon. As a result of its rotation, successive lines are reflected to different levels of the theatre screen represented by "L," thus scanning the entire screen area. The reader will note that this system of scanning is very different from the American systems of television. The makers assert it was planned for largescreen use from its inception, with complete disregard for the requirements of home television. The standard projection arc as the source of light, its makers say, was taken as the point of departure, and all other features were planned to make possible the use of that type of light source. Non-optical portions of the system such as, for example, the television amplifiers, embody no important departures from the principles used by American manufacturers. Synchronization, in scanning is of course maintained by controlling the speed of rotation of the two mirror polygons, "I" and "K." Cleaning Projection Room Wall Surfaces INCREASING use of sound-absorbing material on the walls of projection rooms presents a new problem to projectionists who are concerned about the cleanliness and appearance of their working premises.. Such materials are now often used for the upper portion of the projection room walls, beginning at a height of about five feet from the floor. They catch dust easily and become grimy in appearance. The theatre cleaning staff does not always know what to do about it. One thing not to use is soap and water. These materials are usually sponge-like in structure (to increase their absorption of high-frequency sounds) and soap that has penetrated their pores is not easily flushed away. It may stay there, clogging the pores, reducing their sound absorbing ability, and itself providing a sticky surface that will rapidly catch more dust. No cleansing agent should be used that will not evaporate completely. Alcohol-and-water is usually effective. However, since these materials vary greatly, any cleanser tried should first be used experimentally on a very small area in a remote corner, to make sure the material is not damaged. Alcohol plus ammonia water may also be tried in this way. A More Energetic Agent A mixture of benzine and carbon-tetrachloride, half and half, will prove useful for some types of obstinate stains, but is comparatively expensive. For a more energetic agent, use a solution of water and tri-sodiom phosphate, but only after careful trial, and not too often. This agent will not evaporate completely. Crystals of the trisodium phosphate will remain in the pores of the material unless thorougmy flushed out. They are. however, crystals. as distinct from the gummy filling formed by residual soap. Remember to try all these agents in advance on a very small, hidden part of the surface, to make certain the material is not injured. Many acoustic surfaces can be painted, but not with just any ordinary paint. Most paints, including most "flat" paints, possess a certain amount of "gloss" — that is, give a more or less glossy finish. A paint that has even a small amount of gloss-producing ingredient will tend to bridge over the smaller pores of the material, impairing its acoustic properties. Certain types of "acoustic" paints, made for resurfacing acoustic materials, are on the market. They are essentially truly "flat" paints. Paint purchased locally will serve if it is entirely "flat." The paint should preferably be sprayed on. If it is brushed on, it must be very thinly applied. Avoid Excess Pigment Most paints are made with a white pigment. When color is desired, the painter stirs in an additional, colored pigment. Too much pigment is undesirable. Therefore, either paint the surfaces white or try, if possible, to obtain a paint which contains no white but only pigment of the color desired. Some acoustic surfaces, however, cannot stand any paint at all without loss of their acoustic properties. Before paint is applied, therefore, the manufacturer should be queried. The foregoing remarks anent cleaning and painting apply equally to acoustic wall materials which may be used in the body of the auditorium or elsewhere about the theatre. MAY 1941