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THE PROJECTION LIFE OF FILM* R. H. TALBOT**
Summary. — With the present scarcity of raw print stock, there is need for procedures which will substantially increase the useful life of the film at hand. Prints are rendered unserviceable by damage to the perforations, by mutilation of the edges in shipment, and by abrasion of the surfaces.
The means by which each of these types of film damage can be minimized (and in some cases almost entirely eliminated] will be described. The adoption of only one of these film conservation measures should double the useful life of a print. Universal adoption of all these measures could make possible several hundred bookings of a print.
WEAR LIFE OP-MOTION PICTURE POSITIVE FILM
There is no simple answer to the question "How many times can film be run through a projector?" It has been demonstrated many times that whereas one sample of film may become completely unserviceable after relatively few projections, another sample from the same roll of film may still be in serviceable condition after several thousand projections, depending on the conditions of operation.
It is true that there are certain qualities of the film stock itself which influence its wear life. Much could be written on the relation of the physical properties of the film (tensile strength, tear resistance, brittleness, etc.) to its durability. This relation, however, is one with which the film manufacturer is primarily concerned. The user of film is more concerned with those factors which greatly influence the wear life of the film he has at hand. This paper deals with some of these factors.
Relationship between Pitch of Sprockets, Pitch of Film, and Film Wear.— -If motion picture film were as dimensionally stable as steel, there would be no problem of the relative pitches of film perforations and sprocket teeth; the 2 pitches would always be equal and, consequently, several sprocket teeth would be in contact with the edges of the perforations at the same time. Actually, the pitch
* Presented May 15, 1945, at the Technical Conference in Hollywood. ** Eastman Kodak Company, Kodak Park, Rochester 4, N. Y.
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