Movie Makers (Jan-Dec 1952)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

237 PROJECTOR 960 R pm A PROJECTION TIMER With this electro-mechanical system you can tell not only when — but how much — your projector is out of synchrony FLEXIBLE SHAFT 15/1 SPEED REDUCER ADDED WHEEL I " 1U 64 R pm P P" GEAR " TRAIN TIMER Ejij MINUTE HAND-* SECOND HAND & m?_J A DIAGRAM makes clear (he speed reduction from 960 to 1. IF YOU will look only casually at the projector pictured in Fig. 1, you will note that it has mounted prominently on it a large stroboscopic disc. The function of this disc, of course, was to warn me when the projector was going faster or slower than its intended 16 frame-per-second speed. And this duty the disc quite successfully discharged. But the trouble was, as I tried to synchronize my films and tape recorder, that the strobe disc never told me how much faster or slower the projector was performing than it should have. Thus, when I attempted to compensate for each discrepancy in timing, there was delay in effecting this compensation — and the discrepancy tended to accumulate. The arrangement pictured on this page does away with this difficulty. Basically, it consists of a timer (A) with a sweep second hand, which is driven at a suitable speed by the revolutions of the projector, and an electric clock (B ) , also with a sweep second hand, which is driven in the normal manner by an AC power connection. With both the timer and the clock hands set at a similar starting figure (say 12 o'clock), and then with the projector and the clock both started together, the sweep second hands of the timer and the clock should revolve in synchrony. If the timer hand I driven by the projector, remember) gains on that of the clock, you slow down the projector until both second hands are again in step. If the timer hand lags behind that of the clock, you speed up the projector until synchrony is again achieved. And here is the important JOHN H. WAGNER, ACL improvement: you can tell instantly in either case the exact amount of the discrepancy — and thus compensate quickly for it. How, with unvarying accuracy, is this control effected? In approaching the explanation, let me itemize first the materials needed (other than the timer and the clock) to make up this projector control. These are a 15/1 speed reducer ( C in Fig. 2 ) , which, in my case, I took from an old speedometer head; a length (D) of flexible shaft 3 or 4 feet long; a short length of flexible shaft 2 or 3 inches long; a gear wheel from an old alarm clock, and (of course) a projector. The projector to be used must have an accessible shaft from which its revolutions can be tapped to drive the hands of the timer. In my design a Bell & Howell Showmaster was employed, on which the hand-turning knob revolves once for each frame of film passed and therefore has a speed of 960 revolutions per minute when the projector is running at 16 frames per second. From this knob a connection was carried by the long flexible shaft to the speed reducer so that, on its low-speed shaft, a speed of 64 rpm was obtained (960/15 equals 64), The next step was to remove and discard from the timer its main spring and escape wheel. To replace the escape wheel in the timer's gear train, we selected a suitable wheel from an old alarm clock. This wheel had the correct number of teeth in its pinion so that when the pinion meshed with the wheel which had engaged the escape wheel it would produce a ratio of 64 to 1 between its revolutions and that of the second hand. This added wheel was mounted so that its shaft extended through the back of the timer case (see Fig. 2), where it was connected to the low-speed shaft of the speed reducer by means of the short flexible shaft. You now have a total reduction in speed of 960 to 1 (960 to 64 and then 64 to 1) between the revolutions per minute of the projector shaft and that of the timer's sweep second hand. Since we know that the projector shaft revolves once for each frame of film passed, it clearly will revolve 16 times per second when the pro [Continued on page 247] FIG. 1: At left, the author's setup shows the timer A, electric clock B, speed reducer C and flexible shaft D. FIG. 2: The 1 5 to 1 speed reducer C is seen more clearly with its mechanical coupling into timer's gear train.