[emeritus]

According to a 1970's edition of the "ITT Reference Data For Radio Engineers", in the US, the standard method of showing cine film on TV was to use a projector running at 24 fps fitted with a 5 blade shutter. This gave 120 flickers per second, and so each TV field (half frame) frame would consist of two sequential “flickers”. Thus the first two fields would consist of the same frame, while the third field would consist of the fifth flicker of the first cine frame and the first flicker of the second. With the persistence of the imagers then in use, the existence of a double exposed field would not be noticeable, and as the film ran at its normal sped, there was no change of pitch.

According to something I read in the "Amateur Photographer" at the time, a similar system in reverse was used by the BBC in the 1960's for recording TV onto cine film economically. Rather than running the camera at 25 FPS and recording only the odd (or even) TV fields (the technique used to record the Coronation), it was run at 16 2/3 fps with a pulldown period of 1/50 sec and a shutter speed of 1/100 sec. The film therefore recorded both fields of the first TV frame, the superimposed second field of the second frame and the first field of the third frame, then both fields of the fourth frame and so on. (They published an article on how someone had modified a 16mm sound projector to record TV with sound in this way. It worked, but of course the running cost was horrendous, around £1 a minute at 1960’s prices, when a working man's basic wage was around £10/week if he was lucky.)

For rebroadcast a projector with a three-blade shutter (not the 2 blade shutter normally fitted to sound projectors) running at 16 2/3 was used in conjunction with a conventional 25FPS imager/TV camera. I have a commercial VHS cassette of some 1960’s “Pinky and Perky” programmes that were obviously recorded by this method: stepping frame by frame shows the double exposure of every third frame, which consists of the two slightly different superposed images of what were originally fields of adjacent TV frames.

I use the same technique today for transferring silent 8mm cine film to DVD via a DV camcorder (when I can get one that is still in working order with its manual shutter speed function operational: a 1/50 sec shutter is essential) and the projector must run at as close to 16 2/3 sec as possible to completely eliminate flicker.