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HIGH-SPEED PHOTOGRAPHY EQUIPMENT
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A significant gain in linear film speed may be obtained by attaching a single turn or a spiral of film to the outside of a rotating drum. For a given linear speed the centrifugal force varies as the inverse power of the radius of the drum, but even with large drums the problem of holding the film in place against the centrifugal force is quite serious. A marked mechanical improvement results from placing the film on the inside of a rotating drum, the centrifugal force holding the film in place. The optical arrangement with this system is not in general as convenient, but centrifugal force upon the film is no longer a problem, and the speed limitation is imposed only by the strength of material forming the drum. In this case no gain in linear speed results from increasing the diameter of the drum. The mass of the
Fig. 1 — Scophony high-speed camera. D, rotating drum; F, film; M, multiple mirror; L, camera lens.
drum, considered as a spinning ring, increases with increasing diameter so as just to offset the decrease in centrifugal force. Cameras handling film by this method provide the highest linear film speeds attainable to date.2 Very recently a camera handling film in this manner has been reported by Scophony Limited.3 This camera is illustrated diagrammatically in Fig. 1. A rotating multiple-face mirror M rigidly connected to the drum D carrying the film provides optical compensation for the motion of the film and yields an actual motion picture record. The Scophony camera operates at a film speed of more than 600 feet per second resulting in standard 35-mm motion picture frames at a speed of 10,000 per second. If 8-mm instead of 35-mm frames were used, with an appropriate alteration in the mirror, it would seem possible to obtain 50,000 frames per second by this principle. In effect this has been accomplished in the Suhara1