Movie Makers (Jan-Dec 1949)

MOVIE MAKERS 427 would be simplicity itself. Not all hand testing discs, however, work out this easily, since the majority of projectors revolve the testing knob 16 times in passing 16 frames of film. This figure divided into 120 gives us an answer of 7.5 black segments. COMPROMISE DESIGN This is unfortunate, since there must be a whole number of black segments and a whole number of white in any disc design. There is, however, a workable compromise. The trick is to draw up a disc with an inner and an outer ring of segment patterns — 7 black and 7 white on one, 8 black and 8 white on the other. When such a disc, seen under a neon glow lamp, revolves so that the outer ring appears to rotate about as fast clockwise as the inner one does counter-clockwise, the projector will then be running at the desired speed. So much for stroboscopic discs to be used on your projector. Since they rely for their effectiveness on the pulsations of a neon glow lamp, it should be kept in mind that these discs can be used only in connection with an alternating current supply for the scanning lamp. DISC FOR WIRE RECORDER Now, suppose that I want to set up some system of synchrony between my projector and a magnetic wire recorder— a matter which has been under discussion from various angles in recent Movie Makers articles. How would a strobe disc for such a purpose be designed? Our calculations on this matter must begin with the source of the pulsating light under which the disc is to be scanned. This source is the light beam of the projector itself, which, although it seems to project an unbroken stream of light onto the screen, is actually projecting a beam which is regularly interrupted by the projector's shutter. It is the number of these interruptions for each frame of film passed which is the first important figure in these calculations. The number varies, depending on shutter design, but in my machine it is 3 interruptions per frame. The second important figure is the number of revolutions of the takeup reel on the recorder. On the Webster, for example, this stands at 114 per minute. With these figures in mind, let us now restate basic formula No. 1 : N equals F F, the frequency of the light source per second, now becomes 3 interruptions times 16 fps, or 48 flashes per second; r, the number of revolutions per second, becomes 114 divided by 60, or 1.9 revolutions per second. Substituting these values in the formula No. 1, we arrive at the following: 110 Volt AC/DC Variable Speed Motor th TACHOMETER for EK Cine Special Now you can motor drive your Cine Special with confidence. Tachometer is mounted in clear view of operator. It is calibrated from 16 frames per second to 64 fps. with a definite RED marking for 24 fps. Electrical governor control for adjusting speeds. Steady operation at all speeds. "OFF-ON" switch built into motor base. No adaptors required, except motor-coupling which attaches to camera and couples to motor. Motor shaft equipped with spring steel drive arm which will shear if camera jam occurs. This drive arm is easily replaced. Furnished complete with rubbercovered cable and plugs. Write tor complete details. ^^■S ^* FRANK C. ZUCKCR ii (YflnreRH €ouipm€nT|o. Vi£* 1600 BROHDtUHS n€W aORK CITU '.i.'X. Give Endless Entertainment and Education Model 631MB 16mm Projector For Sound or Silent Films """*■•.,. b$198 50 MOVIE-MITE ... the FIRST precisionbuilt, extra light weight, compact 16mm projector . . . gives you ALL the advantages of finest 16mm projection (silent or sound) at low cost. MOVIE-MITE . . . complete with speaker, weighs only 26 lbs. Universal 25-60 cycle A.C. or D.C., 105-120 volt operation. Write for details. Se /our dealer for demonstration.