jgpo@iwu1c.UUCP (06/30/83)
According to "Electronic Communication," fourth edition, by Robert L. Shrader (a superlative book, by the way), special equipment is needed to synchronize the motion-picture projector and the video camera. I quote: "The TV frame frequency was selected as 30 per second... Unfortunately, both 35- and 16-mm motion pictures have a frame frequency of only 24 per second [here Shrader is assuming sound film; silent films are even worse at 16 per second]. To reduce flicker, each film frame must be produced as two or more fields for both motion pictures and TV. A standard 16-mm projector can be used for TV projection by using either an electronically flashed xenon light or a projection lamp with a special shutter to allow the following sequence of operations with a storage-type pickup tube (vidicon): 1. The film is pulled down into position in the projector. No flashed or shuttered light shines through the film as yet. 2. During the TV vertical blanking-pulse interval, the camera tube scanning beam is blanked out and is returning to the starting point. At this time a flash of light is allowed to shine through the film, projecting the picture on the mosaic. 3. The mosaic retains the electrically charged image of the picture. 4. The mosaic is scanned for one field, and the video signals obtained are transmitted. 5. At the end of the field, during the next vertical blanking pulse and scanning retrace, the projector light is again flashed, projecting the same picture on the mosaic. 6. The second (interlaced) field is scanned, and the video signals obtained are transmitted. 7. During the scanning time of the second field the next frame of the film is pulled down into position. During this frame, because of the difference between 24 and 30 frames per second, there is enough time to flash the projector light three times during blanking pulses before the next frame is pulled down. "In this way, the first film frame is scanned twice, producing 2 fields for the TV picture, but the second frame is scanned as 3 fields. This allows the correction that is necessary to change 48 fields per second for the film to 60 fields per second for the TV picture. [There are 2 fields per frame in a TV picture - John] "Accurate synchronization is required between blanking pulses and the operation of the shutter, or the flashing of the xenon light. This necessitates synchronous motors for the shutters, or a multivibrator- keyed light source synchronized by driving pulses from the sync-pulse generator." And that is spelled $$$. In short, you could probably get SOME kind of an image just by pointing your camera at the screen, but I doubt if it would be very watchable. John