Moving Picture World (Jun 1919)

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June 21, 1919 THE MOVING PICTURE WORLD 1799 tionable, as it is quite possible to arrange an automatic break which will stop the reel almost immediately when the film leaves it, at the same time stopping the motor. But my plan is to use a slow-running rewinder, so that there will be no slapping. I have said, and do now repeat: no film should be rewound at greater speed than 1,000 feet in six minutes, which is at the rate of 166 feet per minute. Even this is entirely too fast. Ten minutes to the thousand feet is fast enough, but I concede six minutes, because of Mr. Shoot 'Em Through. With £. T~/m*£ o* WOOD O/JC 4-, C^DQ frtCCt. *"D SMffi r*OM rr*tW*ITCM <S. "Wej&xr. slow rewinding, even at six minutes to the reel (less than 3 feet per second), it is unnessary that the projectionist watch the process. All he has to do is place the reels on the rewinder, start the motor and go on with his projection duties. The stock objection is that the projectionist should watch the rewinding to detect possible loose patches, etc., but this I deny, absolutely. With a photoplay on the screen, it is nothing less than a crime for the projectionist to be doing anything else under the sun but project that photoplay. Come again, brother. Maybe we won't always agree, but I like a man with ideas, whether I always agree with them or not. From Victoria, B. C. Marvin H. Thoreau, Victoria, B. C, orders lens charts and sends letter, together with drawing of his projection room. The drawing is in lead pencil, and lack of time prevents me from redrawing it in ink for reproduction. Correspondents should remember that drawings MUST be made either with draftman's ink, or at least with a good grade of BLACK ink. If the sketch is a simple one, and of sufficient importance, I may re-draw it in ink for publication, but that is not possible in such an elaborate drawing as friend Thoreau sends in. It would require at least an hour to re-draw it — maybe more. His letter reads: "Send lens charts. Don't need question booklets, have saved all the Worlds since 1911. Am sending carbon stubs as you requested. There is no such thing as a Vancouver Class A' card. It is a 'British Columbia First Class.' I've had one since they made 'em. Was, until recently, a member of Vancouver "local union 348, but hold card in 16S, Victoria, now. Am of the opinion that the place to focus the crater is about one inch on condenser side of the aperture. Seems to me this gives most even screen illumination. A practical aperture lens or short working distance (back focus) objective, with crater _mage located as suggested, should give good results. In cases where lens diameter or long working distance of objective would cause excessive loss with crater image on condenser side of film, it might be practical to advance it somewhat beyond the aperture, but this has tendency to cause ghost or uneven screen illumination. Seeing that I am from your old stamping grounds, Colorado — Canon City, to be exact — deal lightly with me. "As to projection room, last time I wrote was projecting a 22 foot picture at 140 feet, with a 50 foot drop. D. C. supplied by an old Fairbanks-Morse. During the flu scare, a' new projection room was built. Projection now is level, with a 17 foot picture at 88 feet. Screen surrounded by a 3 foot black border. D. C. supplied by a new Double Arc Transverter. Room is 15 feet wide by 9 deep. All wiring in conduit, with rheostats and house dimmers in room above,, controls extended down to projection room. Front wall and inside of all ports dead black. Other walls will soon be black also. Spot port 18x24 inches is kept closed during projection. Between projectors is observation port 10x17 inches, covered with plate glass set at an angle near outside, which gives an 8 inch shadow box. The small observation port (8x12 inches) at right of right hand projector, and the lens ports, will also be glass covered as soon as air intake is completed. Revolving shutters are fitted to the conditions of the theatre. Lens ports also are stopped down to pass only the effective beam. Re-Winder geared down, but no automatic stop — yet. Spot covered to protect eyes, and colored glasses installed in lamphouse door ports so that arc can be observed without eyestrain. All incandescent lamps are so shaded that no light from them can reach the walls above bottom line of ports. Have a powerful pair of binoculars for focusing. Floor is covered with heavy cork linoleum. Transverter is located in easily accessible, well ventilated daylight room. Use Speer Hold Arc lower and Speer regular upper. Condensers meniscus plano-convex. Ordered Bi-convex, but they sent wrong focal length. Spot and stero use A. C. Spot amperage variable, 30 to 60, using National Special A. C. carbons. Current through Ft. Wayne Compensarc. From my chair between projectors I can easily see or reach following: ammeter, voltmeter, field rheostat control, clock, lamp control switches, motor control switches, dowsers, carbon feed handles, string controlling dowser on stero — in fact almost everything necessary to projection, including friction speed control. Am building an arc control which, due to a new principle will, I believe, have them all going South, insofar as concerns simplicity, cheapness and results." Show us, brother, as to the control. Words cost little, but "the goods" delivered is what counts. We wish you success. Your installation seems to be pretty well beyond criticism. Friend boss has given you the things to do with, see to it that you deliver the goods on his screen, not sometimes, but ALL the time. The two switches you ask me, in Projection Experience MOTION PICTURE HANDBOOK For Manager* and Operator! By F. H. RICHARDSON The recognized standard book on the work of protection. Complete descriptions and Instructions on all leading machine! and projection equipment There isn't a projection room in the unlvene m which this carefully complied book will not tare Its purchase price each month. Buy It Today (4 the Copy, postpaid MOVING PICTURE WORLD BI6 Fifth Avenue, New York City Schiller Building, Chicago, III. Wright & Callender Bldg., Los Angeles, Cal. To save time, order from nearest office. a side note, to "guess what they are for," are the shot circuiting switches which act to place the two lamps in series. Please act as my messenger and convey to the members of No. 168 my very best regards. If I said "Vancouver license," it was an error. I knew it was for all British Columbia. Resistance Problem. Frank Gattie, Pheonix, Arizona, member Newport News, Va„ L. U. No. 264, desires light on the following: "This is my first letter to the depart + I SME5 MULTIPLE MULTIPLE SERllS ment, though I have been reading it, and getting good dope from it too. Saw an account of the Vancouver, B. C, examination for projectionists and would like to know how to hook up that bunch of rheostats so as to get 100 amperes from a 220 volt supply. There are three 50 ampere, 110 volt, two 30 ampere, 110 volt, three 25 ampere, 110 volt, and two 15 ampere, 110 volt rheostats. I also would like to know what difference in amperage would result if four 110 volt, 25 ampere rheostats which were connected in multiple series to a 220 volt supply were changed to series multiple. My own idea is that the series multiple connection would give 100 amperes, whereas the multiple would only give 50. Am I right or wrong?" As to the matter of getting 100 amperes out of the rheostats named, I don't myself know whether it could be done, and cannot stop now to figure it out. When 1 wrote the article in question I merely intended to convey an idea of the way things are done. I could not possibly remember exactly what rheostats were actually in use, except that there were several of them, of varying amperage and voltage; also that the examiner said the candidate was asked to figure out what combinations to use to get various amperages. And anyhow, it is a good brain exerciser for the fans, so I'll just pass it along. Can any of you get 100 amperes out of that mess of rheostats, supply being 220. Figuring it out is quite simple. First you will ascertain what ohmic resistance you need for 100 amperes with 220 volts supply. You then figure the resistance of each separate rheostat, remembering that the 110s must be in series groups of at least two. Go to it and let us see what you can get out of it. Remember the resistance of the arc. As to the other matter, why with only four rheostats there would be no difference at all. This for the reason that you could not have but two rheostats in each series of your multiple series, and the series multiple would necessarily amount to precisely the same thing. See drawing. At first glance you might be inclined to say there is no difference, but closer examination will convince you that when it comes to incandescent lighting, for which the systems were designed, there is. I cannot imagine a case where series multiple (parallel series is the correct term) would be used for resistance, though multiple series (series parallel) might be used in case of high voltage and small capacity, low voltage rheostats. In series parallel a number of incandescents were used in each multiple, so that the burning out of one lamp would not have so much effect on the others.