The Moving picture world (November 1926-December 1926)

December 18, 1926 MOVING PICTURE WORLD 541 Bluehook School Answers 540 and 541 Note : — This "School" is designed to arouse interest in the study of those many problems which constantly arise in motion picture projection, AND to cause men to really study the Bluebook and assimilate the vast amount of knowledge contained within its covers. Question No. 540 — Just why is resistance or its equivalent necessary in a projection arc circuit? W. C. Budge, Springfield Gardens, New York; C. H. Hanover, Burlington, Iowa; Al Lehman, Glenside, Pa.; Frank Didiak, Fairmont, W. Va. ; G. L. Doe, "Bill" Doe and John Doe, Chicago, 111.; Allan Gengenbeck, New Orleans, La. ; Charles Curie, Chattanooga, Tenn. ; T. R. Bankerton, Wentzville, Mo.; George E. Lawrence, Sackville, New Brunswick; G. R. Hahn, Memphis, Tenn.; Charles C. Colby, Santa Fe, N. Mex.; T. R. Guimond, Mobile, La. ; D. G. Henderson, ■Quincy, 111.; T. L. Johnson, Lincoln, Neb.; Gilbert Atkindon, Cleveland, Ohio; Albert Hancock, Dallas, Tex. ; William C. Jones, Boston, Mass., and George Barker, Louisville, Ky., all made acceptable answers. Strange as it seems there were in all 114 men who sent answers which were not correct in so relatively simple a matter as this. Hanover says : In order to secure any desired amount of light within range of the optical system of the projector, a certain current strength measured in amperes must pass through the arc, and in order to secure just this amount of current, there must be just enough voltage or electric pressure impressed on the carbons to force the required number of amperes against the resistance of the arc. II there be not sufficient voltage, there will not be the required number of amperes of current flowing through the arc. If there be too much pressure, the amperage will be too great. The purpose of resistance in a proJpcUon aro circuit, or its equivalent, is to reduce the voltage impressed upon the carbons to just the amount of pressure necessary to force the required current "across the arc" against its resistance, plus the resistance (to be very accurate) of the wire from the arc back to the generator. Gentlemen, I dotfi't believe a better, more concise, complete answer could be made to that question. I recommend it even to the serious consideration of those who did answer correctly, though some did so by a very narrow margin. When you have to answer a question such as that, just stop and think. Consider what the rheostat is doing and WHY IT IS DOING IT. That's the answer. One correct answer reads : Resistance in a moving picture aro circuit is necessary as a means to control the current, stepping its voltage and amperage down to worlting requirements. Um, well, yes, that is correct. BUT — and I think you will agree with me — it comes under the wire by a very, very narrow margin. Question No. 541 — If you have an Ju-c burning normally at 60 amperes and you freeze the carbons, what will happen and why will it happen? I think G. L. Doe answers this one best, though several others did very well. Doe • says : A projection arc may be either controlled by a rheostat or be supplied by a generator the windings of which supply a constant, fixed amperage against a considerable range of resistance. I believe the rheostat controlled arc is meant by the question. In either case, however, the ultimate result is the same, except that the constant current generator may be able to handle the matter, whereas the rheostat cannot. The '"case" is this: Taking a rheostat controlled arc for example, the current flow is controlled by (a) the rheostat resistance and (b) the resistance of the arc itself. When the carbons of the arc are brought into contact with each other (frozen) the resistance of the arc, which is a very considerible proportion of the total resistance, is entirely eliminated. The result is, of course, a heavy increase in amperage flow, but without any light production whatever, except for a faint glow of the probably red hot carbon points. The increased flow will (a) overload the rheostat, and (b) probably blow the fuses if the carbons remain frozen for any appreciable length of time. An excellent answer, as I think you will all agree. One of the most valuable features of this "School" is, as I have already pointed out, the fact that those who work out the answers themselves, whether they send them in or not, are able to compare them with the published reply and see where they failed or were weak. Those who are too lazy or indifferent to try to work out the answers, but look religiously for the correct answer each week, really get little or no real benefit at all. Naval Man Is In a Bad Jam JD. S. CILGONE (as nearly as I can • make the name out), U. S. S. Tennessee, writes from San Pedro, Cal., in part as follows : "Am just a beginner in motion picture projection and thought you miight help me. Am interested in the questions asked you and your replies; also in better projection. "I have the job of Movie Operator on the U. S. battleship Tennessee. Have been on the job three months and have learned quite WHY PAY MORE? Roll Tickets Your Own Special Wording 100,000for$15.50 10,000 for $4.50, 20,000 for $7.50 50,000 for $10.00 Standard Rolls of 2,000 KEYSTONE TICKET CO. Dept. W., SHAIWOKIN, PA. The Union Label if you want it Have been printJns Roll Tickets for 10 years and no better can be had at amy price. a bit by myself. I have three projectors, the best being a Simplex. It is new and very easy to handle. Have a Powers Six B which is seven years old. It is badly worn and the frame is not in line with the lamphouse. It makes a man's nerves stand up on end when he tries to project a picture and it is not satisfactory because of worn equipment. "I also have an Acme, which I just plain have to force to run, as the Powers That Be won't buy a new one until the old one is worn out — won't run any longer. I suppose I'll have to be content as long as I am where I am, but when my time is up I propose to become a motion picture projectionist on the outside. Could you give me some advice as to what to study?" Not True Economy May I suggest to the officers of the Battleship Tennessee and to all other Navy authorities that, while waste in property and equipment bought with public monies is reprehensible and should not be tolerated, it is NOT TRUE ECONOMY TO RUN FILMS THROUGH BADLY WORN PROJECTORS. That represents a greater waste because it not only very largely depreciates the entertainment value of the photoplays you project, but also it probably will work more or less serious injury to the films themselves, thus injuring the show of every one using them thereafter. Navy projection equipment is kept in the very pink of condition. Nothing less would be tolerated. Motion picture projection equipment should also be kept in the very best of condition. As to what to study, well Friend Cilgone, while it sounds egotistical it is just a plain statement of fact that the two best things I know of for you to study are the Projection Department of this paper and the Bluebook of Projection, the fifth edition of which will be ready for distribution very soon. The new Bluebook will have more than 1,000 pages, every bit devoted to motion picture projection and equipment. It will likely cost six dollars and may be had from the Chalmers Publishing Company, 516 Fifth Avenue, New York City. A Damaged Screen (Continued from preceding page) You have ruined the surface now, in any event. Why not try paint, as per directions in Bluebook. By renewing the surface, say once in six months, you will, I am sure, get really better general results than with a j metalized surface, which you will naturally, due to its cost, retain in service long aftc its reflective properties have decreased f.' i more tlian you imagine. Mix zinc white with [ turpentine, and just enough boiled linseed I oil to prevent it rubbing up. Add just j trifle of ultramarine blue^so that the paint I has a blue tint while in the can. That is what ' I would try if I were you. Apply as many I coats as is necessary to secure a good | surface.