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MANAGERS AND PROJECTIONISTS
658
edges of the master blade to cut across the light beam faster, hence increased diameter of beam is not of so much importance as with the regular type shutter. Beyond this we do not feel it to be the province of this work to discuss the relative merits of the two types. The Baird projector uses the one-and-a-half-to-one shutter.
GENERAL INSTRUCTION NO. 23— TAKE-UP.— Most
modern projectors are equipped with a take-up device which more or less automatically equalizes the pull on the film, and that a very efficient equalizer is essential is made evident in Fig. 229 in which A represents the lower sprocket of the projector. Suppose with the film attached to the one and one-half inch diameter hub of an ordinary reel as per Fig. 229, and that a lever, G, be attached to the shaft carry
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Figure 230.
ing the reel, if we place a one-pound weight at the end of the lever, it is very evident that the amount of pull on the film at X will be very many times more than the pull on the film at Y, and there lies the kernel of the take-up nut. The lower, or take-up reel is driven by the projector mechanism which runs at a continuous and presumably steady rate of speed, feeding sixty or more feet of film to the take-up reel per minute. You will readily see that under condition X, the reel will have to run very fast as compared to its necessary speed under condition Y in order to wind up the film. We see from this that the take-up reel which is driven by a power having steady speed, must itself run at a speed varying from very fast to very slow, which means there must be slippage somewhere between the driving and the driven members.
One way of accomplishing this is shown in Fig. 230, in