Handbook of projection for theatre managers and motion picture projectionists ([1922])

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MANAGERS AND PROJECTIONISTS 283 possible delay of the show while it is being wound on again, to say nothing of probable damage through contact with a more or less dirty, dusty floor, (b) (Very serious indeed) the increased temptation to "pull down," and pull down good and hard, too, in order to get as much of the film inside the reel sides as possible, (c) The fact that the film may rub against the magazine, thus scratching it and possibly interfering seriously with the operation of the takeup, incidentally requiring an excessively tight takeup tension, which is worse than bad, and a prolific source of damage to the first part of the film through scratching and the tendency to pull the film over the teeth of the lower sprocket, thus injuring the sprocket holes, scratching the film and losing the lower loop. HOW MUCH FILM WILL A REEL HOLD?— We have been asked many times how to figure what number of feet a reel of given diameter, with a hub of given diameter, will hold. This is a question which cannot be answered exactly, because it will depend upon how tightly the film is wound. It is possible to figure it, though we cannot recommend the process for accurate results. • First find average length of film layers, which is done by adding together the circumference of the reel hub and the outside circumference of the film roll, when the reel is full, and dividing the result by two. The result will be the average length, in inches, of all layers of film. Next subtract half the diameter of the reel hub from half the diameter of the film roll. The result will be the number of inches of film, or the "depth" of the film roll from outside diameter to hub. Next you may either count the number of layers of film in one inch, or you may divide 1,000 by 6 (six thousandths of an inch being the thickness of film and emulsion), which will give you the number of layers of film per inch, provided the film be very tightly wound. Counting is best, though, and even that will be unreliable, because of variation in tightness of winding. You now multiply the number of layers of film per inch by the number of inches of depth in the film roll, and multiply that result by the average length of the layers. Divide this by twelve, to reduce to feet, and the final result will be the number of feet of film on the reel, or which a reel will hold, as closely as it can be figured.