International projectionist (Jan-Dec 1956)

VOLUME 31 MARCH 1956 NUMBER 3 FILM and the HEAT PROBLEM By ROBERT A. MITCHELL Heat filters and sometimes water and air cooling are needed when powerful arclamps are used for projection. Otherwise the film may buckle so much that it cannot be kept in focus. MOTION-PICTURE film is essentially "still" film adapted to uses foreign to orthodox photography. The edge-perforated 35-mm film designed by Thomas A. Edison for use in his Kinetograph, the first motion-picture camera, was nothing but George Eastman's snapshot film applied to the novel art of motion-picture photography. Eastman, a photographic genius whose wide interests extended to art and serious music, invented the first practical flexible film in 1889 for his Kodak cameras, and Edison employed this new roll film in the same year. The only significant difference between "still" and movie film, even today, is the slightly thicker base, or emulsion support, used for movie film to give it greater mechanical durability. The support material, popularly called "celluloid" (formerly cellulose nitrate, but now non-inflammable cellulose acetate), is the same for both types of film. The Blazing Arc Spot "Still" film is never subjected to the severe conditions of heat and physical stress prevailing in motion-picture projection. Movie film is spared complete destruction only because it is drawn so rapidly through the blazing "spot" of concentrated arc light. But even the standard speed of 1 % feet of 35-mm film per second is not quite fast enough to prevent film damage in drive-ins and other theatres having the most powerful arc-lamps. Film is exposed to the beam of the arc-lamp frame-by-frame as it travels through the projector gate, or film trap. In projectors having front shutters, each individual film-photograph is "flashed" by the hot arc beam for 1/24 of a second. When rear shutters are used, as in all modern theatre machines, each frame receives two 1/96-second flashes of light — a total of 1/48 of a second. This is just half of the really scorching exposure the film gets in old-fashioned front-shutter mechanisms. The rather frightening combination of intense radiation and explosively inflammable nitrofilm was a necessary condition of theatre projection during the first half century of commercial motion pictures. (Eastman Kodak introduced satisfactory safety film in the late nineteen forties.) The projectionist, unseen showman and unsung hero, lived dangerously indeed before the advent of theatre-release safety stock. He faced most emergencies with a single predominating thought — film fire and its prevention. Human life depended upon his clear thinking and quick action. In the days of nitrate film, the possibility of film fire concerned the projectionist every time an increase in arc power was contemplated, or whenever an old front-shutter mechanism was pressed into service as a "spare." And an accidental slow-down of the projector motor took him to the lamp dowser with lightning speed to avert disaster. The safety of the audience is always the prime consideration. Quality Projection The projectionist is still concerned with the effects of heat on film even though he knows there is no danger of being burned alive or asphyxiated by the fumes of smoldering nitrate film. Eastman safety film burns even less readily than paper. By eliminating the element of danger, safety film allows attention to be devoted entirely to the effects of heat on the quality of the projected images. The popularity of the drive-in theatre and the use of wider screens in nearly all theatres have made the heat problem extremely serious by requiring significant increases in the intensity of the radiant energy concentrated INTERNATIONAL PROJECTIONIST March 1956