International projectionist (Jan-Dec 1950)

The Projection of Safety Film A comprehensive analysis of the comparatively new triacetate (safety) film, including notes on its anatomy and characteristic qualities during projection, plus numerous practical hints as to splicing and general handling to effect optimum results. PROJECTIONISTS generally have voiced a number of gripes concerning the working characteristics of the new triacetate safety film. Significantly, those who praise safety film are not the ones who must project it day after day. Bluntly, the average projectionist is convinced that triacetate film fails to measure up to the performance of standard nitrate prints. Current complaints are sufficient evidence that the first projectionist objections to triacetate prints were by no means expressions of unwarranted prejudice against an innovation. A limited survey of the field indicates rather positively that something is wrong, either with the new film stock itself, or with the way triacetate is processed and handled. Undoubtedly, a more comprehensive poll would substantiate these findings. Triacetate film is superior to nitrate stock in several very important respects, notably in combustion characteristics, resistance to the effects of heat during projection, and permanence. The successful production of a slow-burning and permanent film has been rightly hailed as a distinctly forward step on the score of imperishability and an enhanced safety factor. The Projectionist Viewpoint On the other hand, triacetate stock is slightly inferior to new nitrate stock in tenacity, tear strength, flexibility, elasticity, a tendency to become deformed by stresses and strains, and fewer readily obtainable solvent chemicals from which satisfactory triacetate film cements can be made. These properties of triacetate base do not entirely account for the following projectionist complaints: 1. Triacetate film is more difficult to splice than nitrate film. 2. Splices in safety film come apart too readily. 3. Safety prints are difficult to focus. The complaint that safety prints make it difficult, or in some cases impossible, to obtain good image definition on the screen leaves the writer nonplussed. There is no conceivable reason, all theoretical factors considered, why pictures printed on triacetate stock should be photographically inferior to pictures on nitrate stock. The film base, after all, serves merely as a support for the photographic emulsion. By ROBERT A. MITCHELL Concerning emulsion, the base need only be tough, smooth, and transparent. The exact chemical constitution of the base has no effect on the sharpness of images formed by the developed silver or colored dyes in the emulsion. Oscilloscopic comparisons of 9000-cycle sound recorded on both types of stock show no discernible difference: the wave-form of the high-frequency record is a trifle "fuzzy" on each type. Test films for both picture projection and sound reproduction are usually made on safety stock. This would not be done by the Smpte and other technical organizations if the photographic quality of triacetate film were below par in any respect. Concerning Picture Definition Have projectionists been imagining things? If they have, the writer is also a victim of hallucinations. We are reasonably sure that the film base cannot affect photographic definition on the film ; but we also know that the picture definition obtainable from many triacetate releases is not all that it should be. A number of factors in the projection SHOWING THE WAY A WATERSPOT ON FILM EMULSION DRIES Waterspot Emulsion JJl^^L Gelatine has the unusual property of swelling and shrinking almost wholly in one direction. When film emulsion expands under the influence of moisture, it does so in the single dimension — that of thickness. process affect sharpness of focus, aside from faulty photographic images. Does the cause of "fuzzy" projection lie in extraneous movement of film in the projector gate? A very rapid flutter of the film, for example, may simulate out-offocus conditions so closely as to deceive an observer. Such effects are most noticeable where the heat from extremely highamperage lamps contributes to flutter by frame-embossing the film. All of the available evidence, however, goes to show that film-flutter is relatively rare with safety stock. Focus drift is an entirely different matter. When film is rolled up tightly and stored for a period of hours or days, the phenomenon of cold flow causes it to become deformed longitudinally (especially the layers near the center of the roll). This type of deformation is evidenced by a stubborn curliness. The effect of "cold flow" is easily demonstrated by creasing, or bending, film beyond its "elastic limit." The crease will be permanent. Deformation, Focus Drift Triacetate film base, as now formulated, has only 75% of the elasticity of nitrate base, and is also nearly 9% more susceptible to curl deformation than is nitrate base. The heat encountered by the film during projection results in a lateral deformation which shows up as buckling, another important cause of focus-drift effects. Because triacetate film is less susceptible to the effects of heat than nitrate film, this cannot be considered a major cause of the bad focus characteristics associated with triacetate prints. Focus drift, if progressive and regular, simply requires the projectionist to sharpen the focus a few times during the projection of a single reel. It is not enough to focus sharply only the opening scene of a film having this defect. If attention is not subsequently given to the focus, the concluding scenes in the reel may be far out of focus. Irregular focus drift, often noticed in composite reels made up of several small rolls spliced together, is particularly troublesome. Every projectionist has it to contend with during the showing of previews and other trailer material. Projection with extremely high-powered arcs INTERNATIONAL PROJECTIONIST • October 1950 21