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FILM TRANSMISSION EQUIPMENT Wl GE and RCA each offer a pulsed light projector which elim- inates the need for a shutter and reduces the chances of poor sychronizations by using the standard, vertical sychronizing pulse to flash the projection lamp at the proper time. This illuminant is available for both 16 mm and 35 mm projectors. Probably the question of converting the twenty-four frames of movie film per second to thirty frames of television is one which is puzzling most readers. So before embarking on a description of the equipment, the method used to synchronize the two will be outlined. Pulsed Light System As already mentioned, projectors using this form of illumination are made by GE and RCA. The former calls it the Synchrolite, and the latter the pulsed, or switched light. Synchronization using the Synchrolite will now be described for the GE 16 mm projector. The film is moved past the lens or picture gate in an intermittent movement by a claw which en- gages the perforations in the edges of the film and pulls it down one frame at a time. There are a number of ways of making the claw operate; the oldest in general use is the Maltese Cross or Geneva movement. In this, a cam with four slots and curved sides (so that it does actually look like a Maltese Cross) engages with pins which drive the film pull-down mechanism. Cams em- bodying some modifications of this movement are used in the modern television projector to perform a rapid change of frame between successive exposures. The Synchrolite unit itself is a gas-filled discharge lamp which is, automatically ignited by a pulse from the synchronizing genera- tor which trips a high voltage circuit and flashes the lamp at in- tervals of one-sixtieth of a second. The actual conversion is ac- complished by exposing one frame twice and the next one three times. Reference to Figure 4-6 shows this more clearly and indi- cates the manner in which regular pulses one-sixtieth of a second apart are designed to provide the catalyst which causes the con- version. Examination of the right-hand section shows that during the time that film frame number one is in the gate there are three