Motion Picture Herald (Jan-Feb 1936)

unfair. The first question demands a detailed description and analysis of one make of arc lamp equipment. If this is to be demanded at all, it should include all arc lamps used for projection. Had the examiner instead asked a question something like this it would have been entirely unobjectionable: What various things should be very carefully looked after when using high-intensity, high-amperage arc light sources for projection? Or, what relation has crater area of an arc light to amount of light produced? Or, given a light brilliancy of 160 c.p. per square mm. of crater area, what is the difference in total light production between a crater 0.25-inch and a crater 0.50inch in diameter? Or, what causes the difference in light quality or tone between a high and a low-intensity light course? Or, name the various light sources available for projection work. Or, explain why the new Suprex carbons produce such brilliant screen illumination when the carbons are of such small diameter. Such questions deal with things the projectionist should know, or at least have a fair knowledge of. It is his business to know them. If he does not, he has neglected his business, since the information is available to him. However, a very competent projectionist might be wholly unable to explain in detail some one individual lamp equipment with which he has not actually worked. As to explaining the operation of the new Suprex lamp, thousands of projectionists have as yet never even seen one and, anyhow, the question is not fair, even though general information about that light source has been laid before them. But all projectionists should be able to answer the question as I have stated it. As to explaining how sound-on-film is recorded and reproduced — well, that is rather needless, is it not ? There are so very many other questions of a more practical nature insofar as has to do with projection. And why question four? If it read, give detailed explanation as to how projector arc lamp carbons are automatically fed toward each other in such manner that a practically constant arc length is maintained, it would be a highly practical examination question. While questions five and six are not foolish, they are very unfair and not properly a part of such an examination. Drawing such diagrams is an engineer's job. I venture the assertion that not one projectionist in a hundred could draw such a diagram, nor is it any part of his business to know how to do so. Were this the question : Explain the action of a full-wave and a halfwave rectifier, it would be legitimate. Assuming the questions to be correctly stated, it would seem that the Atlanta examination should be revised, and rather sharply. I am a firm believer in thoroughness in projection, but the bread and butter of men, women and children depends upon the ability of the men to get employment, therefore examinations should be very carefully guarded from questions that are in any way unfair. Questions should deal only with such things as competent projectionists may reasonably be expected to answer. They should be largely confined to questions dealing with practical work in projection and explanations of such things as rotating shutter action, intermittent movement action and its speed with relation to passage of light and to flicker ; why increased current produces additional light (that might bring out some surprising answers) ; what various effects dirty lenses have and why ; why lowintensity lamps produce so much more light per watt than do the old style or even highintensity arc ; the action of the exciter lamp, its optical system and the photocell; just what current "amplification" really consists of ; what an amplifier vacuum tube consists of and how it operates; why the utmost cleanliness of sound apparatus is essential to good results ; how film should be cared for while in a theatre projection room ; the essential features of proper rewinding of film ; the essentials of a perfect film splice — and other questions of a practical nature, varying the questions, however, with each examination. OPERATING DATA SHOULD BE SUPPLIED FROM NEBRASKA comes this message: "Our manager is going to purchase two Sterling lamps. I have been unable to find the name and address of the makers of these lamps in Better Theatres, or any information about them anywhere — the kind and size of carbons, distance center of mirror to aperture, kind of mirror, distance center of mirror to light source. And as the lamps are secondhand I am afraid no instructions will accompany them. "We now are using low-intensity lamps, RCA sound (P.G. 30). The house seats less than 900. We are going to use copper disc rectifiers, concerning which I also am unable to get any information at all, and the manager refuses to supply any data except what I have told you. I naturally want to get enough dope so that I can handle the equipments efficiently when they are installed. Where can I get the new Bluebook ?" You can order the new Bluebook from the Quigley Book Shop, 1790 Broadway, New York City. Price $5.25. It will give you complete information on copper disc rectifiers. You will be able to obtain full instructions from the manufacturers of the Sterling lamp. Your manager is pursuing a wrong course. If he proposes to install new and different equipments, he should see to it that you are provided, in advance, with every possible bit of information concerning them. However, aside from proper connections there is little information you need about the new copper disc rectifiers. They require no attention whatsoever except to keep them free from dust and dirt and to inspect them occasionally — say, once in 90 days — to see that their clamping bolt nuts are all tight. Managers should realize that in order to handle a light source equipment or anything else efficiently and well it is neces sary that the equipment be thoroughly understood by the projectionist. It is therefore good management to see to it that the projectionist is, as far as possible, well posted on both the theory upon which equipments depend for their operation, and the practical side of operation — how to so handle the equipment so that the best possible results will be had, and had at the lowest possible cost. KINDS OF FILTERS AND WHAT THEY DO JOHN L. GREGERSON of Wilmington, N. C, asks, "Will you please explain exactly what a low-pass, a highpass and a band-pass filter is? Just what do they really do?" A high-pass filter is an electrical network that will either largely reduce the value of, or wholly exclude, all frequencies below a predetermined value. In other words, it will permit only frequencies above a certain value to pass through a circuit which it controls. A low-pass filter is exactly the opposite, permitting only frequencies below a certain predetermined value to pass. A band-pass filter is a network so constructed that it excludes frequencies above and below certain values. There also is what is known as a "narrow band filter," which is a band filter that passes only frequencies of a very narrow range, excluding all those above or below the predetermined points. However, please understand that when I say "excludes all" I do not mean that quite, since close to the dividing line the frequencies said to be "excluded" are usually not quite, but their power is very largely reduced. Those further from the aforesaid line are to all intents and purposes totally cut off. GRATITUDE— BUT IT WAS HIS IDEA! T. a. wilkenson, projectionist of the Alamo theatre in Belleville, Tex., writes, "Here is what is perhaps your first letter from a projectionist not containing a question — the letter I mean — though probably later ones will. I cannot remember when I first began reading your Comments, but believe you me I've not missed one since. Also from friend employer I borrowed a Bluebook, issue of 1927, which has helped me a lot. In fact, to show you how much I think of the old one, I attach a P.O. money order for $5.25 for the new edition. "I have been trying to project motion pictures and sound for a little more than five years, but must admit it has been just trying. But at last I have, because of your writings, come to realize (I think I do realize at last) the importance of projection as a profession. At least I know some of the differences between motion picture-sound projection and machine operation. "I am proud to say that our small theatre in a small town (population, 2,000) enjoys the reputation of being competently 28 Better Theatres