Motion Picture Herald (Mar-Apr 1947)

This, of course, is based on a good grade of optical glass. Now for question two: Well, Mr. Lee, you will always have arguments about light-up time. If I asked twenty projectionists, I would get twenty different views. Each one would have his argument as to why. So I will answer this one the way I like it and the way the majority of my boys work. I think the one-minute period is the best. It gives your arc a chance to settle down. As to looking for the cue, that is up to the individual. (Hope this doesn't cause you any trouble with your fellow workers!) Once Again: Throw Is No Screen Light Factor it has often been mentioned in this column that the length of throw does not affect screen illumination. The size of the screen determines the illumination at a given arc wattage. I think there still must be some confusion on this subject (as there has been since projection started). Let's go over this ground yet again. The length of throw, or distance from the projection lens to the screen, has no bearing on the intensity of the light inci dent upon the screen (if, of course, the air through which this beam passes is sufficiently free of dust, smoke, fog or other foreign particles as not to diffuse or refract the light, and if the lenses used have equal power of transmission) . For example, let us suppose we have a picture 27 feet 9^2 inches wide. A 3^-inch E.F. lens 110 feet from the screen will project this size of picture with a standard sound aperture, and so will a 5^2-inch E.F. lens 185 feet from the screen. If both the 3>i-inch E.F., and 5^-inch E.F. lens have the same relative aperture and the same number of optical elements, made up of the same kind of glass, there will be no difference in the light on the screen 110 feet or 185 feet away from the lens. The misconception surrounding the idea that the length of throw has a direct bearing on the amount of light on the screen comes from the fact that if we place an object — say, 4 inches from an open light source, such as a candle — we will have onefourth as much light falling upon it as we have at 2 inches from the candle (unfocused light falling upon an object decreases by the square of the distance from the light source to that object). Another factor which has led many to believe that a longer throw causes less light to fall upon the same size of screen is the fact that long focal length lenses usually have a lower relative aperture than short focal length lenses, and do, for that reason only, transmit less light. Should Sound Service Men Include Projection? I have also been asked to give my opinion on how much field a sound engineer should cover. In other words, should our sound service man be responsible for all the booth equipment, or should he stick to the field he was originally chosen for. Well, here's the way I have got it from most sound engineers whom I have spoken to about this: A good portion of the sound men are college graduates in the field of electrical engineering and they feel quite capable of taking care of the circuits in a sound system, but many of them tell you outright that they never paid much attention to projectors. I do not mean that some of the engineers are not capable of doing this work, because like any person mechanically inclined, they would delve into a projector for their own satisfaction or to help out a projectionist who is in trouble or maybe doesn't understand it as well as he might. If these conversations with sound service men have produced worthy evidence, perhaps a sound service organization should conduct sound service and let EVERYTHING FOR DRIVE-IN THEATRE OPERATION Drive-in theater operators look to DeVry for more than dependable moderately priced projection and amplifying equipment. DeVry's new IN-CAR SPEAKERS for drive-in theaters are another outstanding contribution by DeVry to the Exhibitor's and Projectionist's goal — the perfect show. DeVry IN-CAR SPEAKERS permit closed windows in bad weather; provide individual volume control to patron's taste; confine sound to immediate theater area, eliminating community complaints; give farthest-parked patron uniform synchronization of sound with action. Don't delay. . . . Place your order for IN-CAR SPEAKERS now and assure on-time delivery. Send for specifications and prices on DeVry theater projector and sound systems, too — "The right pair to draw to for a full house." 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