Moving Picture World (Jan-Jun 1910)

-1-4 THE MOVING PICTURE WORLD OPERATORS' COLUMN. QUESTIONS AND ANSWERS. Conducted by F. H. Richardson. Current and Rheostat. — Kansas City, Mo., wants to know how much current he will get through two 18-ampere rheostats in multiple, with two in series on a loop, pressure [io volts, Presumably he means that d of the loop i connected ahead of the multiple and the Other behind — thai i tu say, one end is connected to the wire between the two in multiple and the main switchboard and the other between the two in multiple and the lamp, so that he will the full current of the multiple, also the full amount supplied by the series. Through each rheostat in multiple he will, of course, gel the capacity of the coils, viz.. 18 amperes, or 36 for the two. Through the series he will get about io}4 amperes. Tt is figured as follows: Seventy volts pressure divided by 10 amperes gives 3 1-3 ohms resistance to the rh 1 at . or 6.66 ohms for both. Seventy volts divided by 6.66 gives approximately ioy2 amperes, the current How through the two rheostats in series. The total current then would lie 36 plus ioy2, or 46J/2 in all. The reason for using 70 for the voltage is that the arc itself gives about 40 to 45 volts drop, leaving 70 to 75 to be taken care of by the rhei 'Stat. Projection Troubles. — Pittsburg, Pa., writes, in part, as follows: "I take the liberty of addressing you to sec if you can locate my trouble. You are helping others, and 1 thought I would cast my lot with theirs. Am using Power's No. 5 machine, purchased last September, and from eighteen inches to two feet of the left side of the picture appears very rainy." Frankly, your case has puzzled me more than anything which has come up in a long time, but I have finally concluded you are probably mistaken in calling what you see on the screen "rain-marks." I am inclined to believe it is your shutter which is at fault and that you have what we call a travel ghost on a small portion of the picture. This is white streaks flashing up, down, or both, especially noticeable on titles. It is the result of the shutter being set wrong or else too narrow. Now, I want you to make the following experiments, carefully noting results, and report to me: First, throw the clear, white light on screen with machine standing still. If you notice the streaks, then the trouble is either in the screen (curtain) itself or in the projection lens. Next put in a film, frame clear down, and run a few feet, carefully noting the result. Next, frame clear up, run a few more feet of film and carefully note results. Next, frame midway and do the same. Examine shutter carefully and see if there are, by chance, any holes in it or if it appears that any of the shutter has been cut off. Rain-marks are produced by scratches in the film and I know of nothing else that will produce them. Holes in the shutter might possibly make a sort of imitation. I shall await your report with decided interest. Getting a White Screen. — Clay City, 111., asks what is the matter when there is a dark spot (ghost) in center of curtain, which may be removed by pulling lamp back from condensers, but when this is done there is a dark circle around the outer edge of picture. He asks if the picture (12 x 14 at 56 feet) is too large for the throw. No, the picture is not too large for the throw. You have a 3/'2-inch projection lens and should have two 6l/i condenser lenses. Measure your condenser lenses and, see what they really are. Pin a white sheet of paper to a wall opposite a ■window. Hold lens with flat side to wall and move back and forth until a clear, sharply defined picture of the window is propected on the paper. Then measure from flat surface of lens to the wall. This will be the focal length of the lens, which should be about 6l/2 inches in your case for both lenses. Before getting other lenses, however, try sliding your lamp-house forward and back. A ghost may sometimes be removed thus. It is also barely possible the trouble is in your projection lens itself, but I do not think so. Condenser Breakage. — Santa Paula, Cal., asks what to do to stop his condensers breaking. Says he has tried 6^2 and 7Y2 lenses, but does not tell me his picture size and throw, therefore I cannot say what focal length condenser he should have. Says room has no draughts and he has tried covering lamp-house with asbestos box, but lenses break as fast as he can put them in. Says lenses are loose in ring It is wellnigh impossible to tell, sometimes, just what is causing condenser lenses to break, even when one is right there. It is likely, however, that there is excessive heat in your lamp-house, and this excess may be caused by failure to clean out the screen in top of lamp-house. Evidently you have tried to avoid practically all ventilation of lamp-house Try ample ventilation once. More condenser lenses are broken by lack of lamp-house ventilation than by too much. m out the screen in top of lamp-house, and, if not forbidden by local law, open up the back of the lamp-house as well — wide open, if you can. There is no more danger of netting anything on fire by the back of the lamp-house being open than there is of setting fire to the Atlantic Ocean lint with ample ventilation have the vent holes in condenser mount open, also. You ask directions for making temporary announcement slides. You will find directions on page 337, March 5th I6sue, for making very satisfactory slides with a typewriter 1 hey may also be written or printed on glass with a fine pen and India ink, first thoroughly cleaning the glass. Also they may be punched out of cardboard with one of the letterperioral ing machines. Machine Adjustments. — Xew York City, X. Y.. propounds the following, all on one lonesome postal card. I will answei by number: (1) Is it advisable to set the flywheel in tight against the bushing or leave some slack? (2) Should the intermittent sprocket be set in tight against the apron, 01 a little loose? (3) How often do the eccentric bushings wear out?' 141 Is 3 in 1 oil suitable for safety shutter? (5) I low often should the entire machine be oiled? (1) Set it in tight, but not so as to bind. (2) Don't know what you mean. (3) Depends on hours you run the machine per da}' and grade of oil. etc. Renew them whenever the >haft gets loose in the bearing. (4) I never oil the fire shutter itself: it is not necessary. The actuating mechanism should be oiled and the oil you name is all right for that purpose. (5) Depends on circumstances. Aside from the intermittent, which should have a drop of oil every 2,00c feet of film, any moving picture machine bearing ought to run ten reels of film, at least, without oil, assuming that good oil is used. This does not apply to some makes of fireshutter governors, however. Use judgment and common sense in the matter of lubrication. No hard and fast rule can be laid down. F. H. RICHARDSON.