International projectionist (Jan 1961-Dec 1962)

Knowledge of Equations, Ratios Helps in Projection Room Here's How to Use Them BY JOSEPH HOLT Member, IATSE Local 428 Recently we detailed a method by which lens focal lengths might be computed by the simple multiplication of the Cinemascope prime lens by a given factor. Our purpose had been merely to render the job as easy as possible, but we have since learned that there is some confusion in the minds of projectionists who may not have handled any problem more complex than the computing of payrolls for the projection room in a good many years. This article will attempt to detail how easy it is to use simple equations and ratios in the calculation of various problems encountered in the projection room. Consider this statement: % = %. What we have actually said, is this: "If 1 be divided by 2, the same answer is obtained as when 3 is divided by 6." This is a simple enough condition, but it is surprising to consider that all problems wherein three of four factors are a known quantity, we may readily obtain the fourth. The easiest way to do this is the substance of this paper. Let it be assumed that we did not know the quantity of 6 in the example cited. We might have written it %=3/X. To solve this type of statement, it is necessary only to multiply the bottom quantity by the top quantity on the opposite side of the = sign. In the example given, we would obtain the following: 1X=6 (1 times X=2 times 3). Thus it is easy to see that the unkown quantity is 6. Another way of writing this would be 1:2=3:X, which is read "one is to two as three is to X", and we have the simple statement of a ratio. Let it be supposed then, that we have something like the following: 2:8=6:X. To solve this type of statement, we must multiply the two quantities on the end (called the extremes) and the two figures in the center (called the means). In this example, we would then multiply 2 by X, and set down the result, 2X. Then to complete our job, we multiply 6 by 8, and obtain 48. Our next step is then to write "2X=48". We then divide the quantity on the right hand side of the = sign by the figure which precedes X. In this case, 48 divided by 2 gives us an answer which tells us X=24. We can test this simple example by writing % = %4. Naturally, we know that %==%, as does %4, but we can check problems which are not readily ob Norelco PROJECTION EQUIPMENT Available from leading theatre supply dealers North American Philips Co., Inc. Motion Picture Equipment Division 100 E. 42nd St., New York 17, N.Y. BOOKS ON ELECTRONICS . . . WORLD FAMOUS FOR TECHNICAL EXCELLENCE Learn the "picture-book" way! You can master the basics of electricity, electronics or television with these easy "learn-by-pictures" courses. Hundreds of bold, dramatic, informative, specially prepared illustrations make ideas easy to understand. 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