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TECHNICAL FILM PROBLEMS
TECHNICAL PROBLEMS OF EDUCATIONAL CINEMATOGRAPHY
BY
Dr. Ernest Rust,
Zurich.
THE universal diffusion of educational films is impeded not merely by pedagogie and organizing difficulties, but also by a number of technical obstacles. Whether the film is suitable and effective for teaching purposes depends largely on satisfactory technical conditions, and also on accurate and methodical production, accompanied by such organization as will ensure that the film is properly used and properly supplied. Technical questions arise in connection both with the film and with the projection machinery, both with the screen and with the darkening of the hall.
The Film. Matters of special
technical importance in connection with the film are the material on which the image is printed, the dimensions, the system of perforation, and the perfection of the photographic image.
(a) Material. — The modern film is made either of celluloid (cellulose nitrate with camphor : nitrate film), or of acetyl cellulose (cellulose acetate : acetate film), or of cellophane (cellulose : ozaphane film). These different materials resemble one another inasmuch as they can readily be converted into thin, pliable ribbons, trasparent as glass ; but there are fundamental differences in make up.
The nitrate film possesses a greater degree of resistance to pull, and retains its flexibility longer. It is, however, highly inflammable,
burning with a powerful flame, and as soon as it is heated to a given temperature, even if no air is admitted, it decomposes, giving off poisonous gases (nitrogen dioxide, hydrocyanic acid) and evil-smelling vapours which, when mixed with air, are liable to produce a violent explosion. Notwithstanding these bad qualities, the nitrate film, on account of its resistance and flexibility, is used almost exclusively as the material for normal 35 mm. films.
The acetate film actually begins to decompose with the formation of bubbles on the surface, and liquifies at approximately the same temperature as the nitrate film, but without giving off any particularly poisonous gases. It neither ignites nor burns easily. Held horizontally and lit with a match, it generally goes out of its own accord. Hence this kind of film is less dangerous in case of fire than a light cotton fabric. On the other hand, it is less resistent to strain than the nitrate film, and it hardens if kept in a dry place. For these reasons, it cannot long resist the pull of the normal projection machinery, and as in addition, it is more expensive, it has not yet been possible, for economic reasons, to substitute this film for the nitrate in the case of normal dimensions. As a reduced size film, and so subjected to less mechanical strain, it lasts as long as a normal film lasts with normal machinery. Since the producers of sub-standard films have under taken to use only safety films, that is to say, materials