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November, 1950 sandvik and veal : films for television 153
Cameras for Kinescope Photography.
The cameras that are required to photograph the 30-frame television picture on to 24-frame film must, of necessity, be precision instruments. One of these cameras is shown in Fig. 10. It is a 16mm. camera driven by an 1,800 r.p.m. synchronous motor usually powered from the same 110-volt A.C. source as the television station's synchronizing generator. The camera is supplied with a 50-mm. Kodak anastigmat lens which is focused on to a 2.5 by 3.5-inch television picture on the face of a 5-inch Kinescope tube. The film-transport mechanism utilizes an 8-tooth pull-down sprocket operating directly below a nylon film gate, highly polished to minimize gate friction. The camera shutter has a closed-shutter angle of approximately 73 degrees, shown in Fig. 11.
In the transfer of 30-frame television pictures on to 24-frame film it becomes necessary to utilize six television frames for film pull-down time. This requires the camera to combine the film picture precisely from two television fields in every other film frame, as shown in Fig. 12, that is, film frame No. 1 is exposed in exactly 1/30 of a second and includes information from television fields No. 1 and No. 2. During the pull-down time of film frame No. 2,
Fig. II. Eastman Television Recording Camera snutter.
approximately one-half of television field No. 3 has passed, and the remainder of this television field is recorded on film frame No. 2 as is television field No. 4 and part of No. 5 to complete this film frame. This means that film frame No. 2 has been combined in the middle of the picture. Film frame No. 3 is recorded from television fields No. 6 and No. 7 without being combined from two television fields. Again, the film must be moved to film frame No. 4, which is recorded from part of television field No. 8, all of field No. 9, and part of field No. 10, and so forth, each successive frame being combined in the centre of the frame.
Frame Combine Matching.
To accomplish the combine in the centre of the picture and eliminate banding or combine marks, it is necessary, after the correct lens opening has been ascertained by test exposure recordings, to reduce the shutter angle to minimize shutter banding. The shutter is normally supplied too large, allowing for adjustment. When negative film is used, banding will probably be recognized on the film as a light streak across the film frame. This light streak indicates