Technology
NTSC television images are scanned at roughly 60 Hz, with two interlaced fields per frame, displayed at 30 frames per second.
A kinescope must be able to:
- Convert the 30 frame/s image to 24 frame/s, the standard sound speed of film cameras,
- Do so in a way so that the image is clear enough to then re-broadcast by means of a film chain back to 30 frame/s.
In kinescoping an NTSC signal, 525 lines are broadcast in one frame. A 35 mm or 16 mm camera exposes one frame of film for every one frame of television (525 lines), and moving a new frame of film into place during the time equivalent of one field of television (131.25 lines). In the British 405-line television system, television ran at 25 frames—or more correctly, 50 fields—per second, so the film camera would also be run at 25 frames per second rather than the cinematic film standard of 24 frames.
Therefore, in order to maintain successful kinescope photography, a camera must expose one frame of film for exactly 1/30th or 1/25th of a second, the time in which one frame of video is transmitted, and move to another frame of film within the small interval of 1/120 of a second. In some instances, this was accomplished through means of an electronic shutter which cuts off the TV image at the end of every set of visible lines.
Most U.S. kinescope situations, however, utilized a mechanical shutter, revolving at 24 revolutions per second. This shutter had a closed angle of 72° and an open angle of 288°, yielding the necessary closed time of 1/120 of a second and open time 1/30 of a second. Using this shutter, in 1 second of video (60 fields equaling 30 frames), 48 television fields (totaling to 24 frames of video) would be captured on 24 frames of film, and 12 additional fields would be omitted as the shutter closed and the film advanced.
Because television is a field rather than frame-based system, however, not all the information in the picture can be retained on film in the same way as it can on videotape. The time taken physically to move the film on by one frame and stop it so that the gate can be opened to expose a new frame of film to the two fields of television picture is much longer than the vertical blanking interval between these fields—so the film is still moving when the start of the next field is being displayed on the television screen. It is not possible to accelerate the film fast enough to get it there in time without destroying the perforations in the film stock—and the larger the film gauge used, the worse the problem becomes.
The problem of adapting the way the image is either displayed or captured on film, to get around the above, was solved in various different ways as time went on—improving the quality of the image.
Read more about this topic: Kinescope
Famous quotes containing the word technology:
“One can prove or refute anything at all with words. Soon people will perfect language technology to such an extent that they’ll be proving with mathematical precision that twice two is seven.”
—Anton Pavlovich Chekhov (1860–1904)
“If the technology cannot shoulder the entire burden of strategic change, it nevertheless can set into motion a series of dynamics that present an important challenge to imperative control and the industrial division of labor. The more blurred the distinction between what workers know and what managers know, the more fragile and pointless any traditional relationships of domination and subordination between them will become.”
—Shoshana Zuboff (b. 1951)
“Radio put technology into storytelling and made it sick. TV killed it. Then you were locked into somebody else’s sighting of that story. You no longer had the benefit of making that picture for yourself, using your imagination. Storytelling brings back that humanness that we have lost with TV. You talk to children and they don’t hear you. They are television addicts. Mamas bring them home from the hospital and drag them up in front of the set and the great stare-out begins.”
—Jackie Torrence (b. 1944)