Motion Picture Herald (Apr-Jun 1931)

128 Better Theatres Section April 11, 1931 vibrations which move in every direction. Through an ordinary pane of glass these vibrations will of course pass, but a polarizer is so made that it will permit only the passage of light vibrations of one direction — light vibrations which correspond to the light vibrations of the rope. Now when the light comes forward, striking the polarizer, the polarizer operates to cut out all the vibrations except those moving in one plane (the rope vibration), so that only these vibrations mav enter into the liquid in the cell {A in Fig. 1). "And now we come to the analyzer, which is another polarizer set at right angles to the first one, so that, as you may understand from what has been said, none of this light will pass through so long as, to use an understandable expression, its vibrations are up and down. The 'gate' has been turned on its side. However, if the light beam in the liquid can be so rotated that its vibrations will be sidewise instead of up and down, then of course all the light will pass through the analyzer (the gate laid on its side) or, put in another form, through the second polarizing prism. Going a little further than this, the amount of light that would get through the analyzer would be in exact proportion to the amount that the beam of light was rotated. "That is where our charged plate and liquid get in their work, for the light beam will be rotated in exact proportion to the amount of charge in the plates at each ten thousandths of a second. Remember that this charge is varying constantly with the current picked up from the air." There, gentlemen, I believe that is about as clear as this matter can possibly be made to the layman. If there is no charge in the plates, then no light can get through the analyzer. If the plates be charged at maximum, then all the light would be passed through. TYPES OF PROJECTION EQUIPMENT SOME ADVICE is Wanted by Ben J. Kubly of Monroe, Wis., and since the answers to the questions he asks may be of interest to many others, I believe he should be answered through the department. He says: "I am to have charge of projection in a new 900-seat theatre now being constructed by my employer, C. J. Soltz [possibly it is Soetz. — Ed.]. The seats of this theatre are all on one side. I would like very much to have your advice as to what is the best arc and generator to install. Naturally Mr. Soltz desires to install equipment which will be the most economical in manitenance and at the same time handle all present day needs, as well as provide special reserve capacity for possible future developments. The projection distance will be approximately 108 feet. Size of the porous sound screen is not yet definitely decided, but it will be either 18 or 20 feet. Projection angle very nearly zero. "We want to know if the lamps should be high intensity rectifier lamps, or low intensity lamps. The motor generator must be capable of supplying current to two projector arc lamps and one spot, which latter may be replaced with a combination color and effect projector. "Would a color effect projector with a spot lamp be effective at the distance of 108 feet? An 80-160 generator and high intensity lamps have been recommended. Would this generator be large enough to handle combination effect projector in case THE ENGINEER FOR MORE than 20 years this department has from time to time directed the attention of designing engineers to what has seemed to be a very mistaken policy as applies to one phase of their procedure. Ever since the motion picture a spot lamp was replaced with one later? "I realize that you cannot specify any special equipment. However, our equipment is already chosen. All we wish to know is what is the best type and capacity." The first thing to determine is the size and character of the screen, since that determines the amount of space it would be necessary to illuminate. The projection angle will be approximately zero, therefore there will be no appreciable distortion, and (silent picture size) an 18-foot picture would represent 243 square feet of surface, whereas a 20-foot screen would have 300 square feet of surface. Hence, in order to secure an equal brilliancy on a 20-foot screen, it would be necessary to have about 25% more light. Personally, I am not a believer in big pictures, except in very large theatres. A well illuminated 18-foot picture would, in my opinion, be the better of the two for this theatre. If my memory serves me right, the 6,000-seat Roxy uses only a 22footer. It is not a good box office policy to under-illuminate a screen. However, it also is not the best policy to over-illuminate a screen either, and just where the limit should be in any particular theatre depends upon a good many things, the first of which is the amount of illumination in the auditorium itself, and the amount of extraneous light which is permitted to reach the screen. The best advice I can give is what I, myself, would do in a theatre of my own — if industry began it has been, except for some few isolated cases, the practice of engineers engaged in designing apparatus intended for use in projection, to proceed with the development of such apparatus, either entirely without consultation with I owned a theatre. I would install motor generator equipment of ample capacity. An ample capacity involves a greater first cost, but unless the thing be carried too far, the machines of ample size will operate just about as efficiently as machines working at their capacity, and more efficiently than overloaded machines. Also, they will last a very much longer time. I would then communicate with the manufacturer of the lamp I proposed to install, setting forth the distance from screen to rear row of seats and the width of seating space, and also advise him so far as possible as to the length of the auditorium. I would tell him the size and kind of screen. I would tell him whether I wanted a highly or a moderately illuminated pictue. I would then take the equipment he advised. There is no one who is better acquainted with both the capacity and possibilities of performance than the manufacturer himself. Always remember, however, that in order to give intelligent advice, the manu ) facturer (or anybody else) must have full j and complete information. First decide upon the size and kind of screen. Send that information, together with all the other things I have named, to the manufacturer. Personally, I am of the opinion that the low intensity lamp would give plenty of illumination, but as I before said, I do not know what the special conditions in this particular theatre may | be involved to an extent sufficient to in I fluence choice. I practical projectionists, or with consultation so incomplete that it was without much practical value in the actual projection work of the theatre. The inevitable result of this mistaken policy has been that pieces of apparatus AND THE "PRACTICAL PROJECTIONIST" I