Construction of Film‐loop Programs: A New Twist

Abstract

Despite the use of preventive devices, film-loop programs sometimes attain an embarrassing length. A simple strategy halves the length of a loop without altering the program in any way. This consists of constructing the loop in the form of a Mobius ring by twisting one end through 1800 before splicing the two ends together. The program can then be punched in two halves on opposite sides of the center line of the film. Since a Mobius ring has only one continuous side, the complete program can be presented by circulating the loop through the programmer twice. Since in effect this strategy involves adding a second channel to a film loop of half the length, it is necessary to alter the programmer so that it will be operated by punched holes at the side, rather than at the center of the film. This requires that the film sprocket on the programmer be offset by the same amount the punched holes are offset from the center line. In the case of 16-mm film, offsetting these by 2 mm is sufficient. This strategy can be adapted to film programs involving more than one channel by offsetting the channels an appropriate amount. This technique in no way interferes with either the life or serviceability of film-loop programs. A. M. LYSONS

A TECHNIQUE FOR PROGRAMMING LONG INTERVAL SCHEDULES1

“…The main difficulty, in our experience, with the buffer box is that occasionally a tape will "crawl out" of the box. Lysons and Lander (1968) suggested mounting the hole reader on one side of the film then twisting the film to form a Mobius strip. By punching holes on one half of the film the effective length of the film is doubled.…”