International projectionist (Jan-Dec 1948)

. — M 1 |:l! V n. I riw ft * Up if T i ~'w mi ! • 1 II 1 * ■ » ^ •-*--» •»■ y I ill | ; ■ "mil I 1 ^ 35-mm processing machine at Kodak Park often gives rise to in-and-out of focus of images on the screen. The exceedingly low rate of shrinkage of the new safety base indicates that film on this stock should be substantially free from "buckle." The new safety base shows a greater resistance to the effect of moisture and humidity than the acetate propionate safety base or the old acetate safety base, and, in fact, approaches the values of cellulose nitrate in this respect. The low resistance to water of the early acetone soluble acetate base frequently gave rise to troubles in processing, often resulting in film distortion. The acetate propionate type was an improvement in this respect but was still considerably less resistant than nitrate film. Extensive laboratory tests and large-scale trade processing tests have shown the new base to be satisfactory in this respect. Projection Quality Factors The projection quality of the high acetyl acetate safety film has been tested both in the laboratory and in theatres. Exhaustive wearing tests in the laboratory under carefully controlled conditions indicate that the new safety film is a distinct improvement over the acetate propionate type, but still slightly inferior to the best nitrate. This is due in part to the slight difference in physical properties, which has been mentioned, and in part to the lower shrinkage values of the safety film as compared with the nitrate. It should be recalled that the presently used intermittent sprockets on projectors give best mechanical wearing results with films which have undergone a shrinkage of as much as 1%. The lower shrinkage of the high acetyl acetate safety film, therefore, is a disadvantage in this respect. As the new standard 0.943" diameter intermittent sprockets gradually replace the existing intermittent sprockets, this disadvantage of low shrinkage will disappear and the wearing property of the high acetyl acetate safety film will exceed by a considerable extent the wearing quality of the present nitrate on the present 0.935" intermittent sprocket.* The projection quality of the new type of safety film has been found to equal that of nitrate film in screen steadiness and appearance. At moderate amperages, such as from 50 to 70, no difference could be detected between any of the film types — the previously used acetate propionate, the high acetyl, or the nitrate. At arc intensities of 175 amperes, however, the superior performance of the higher acetyl type over the acetate propionate is marked. After projection at high arc intensities the high acetyl acetate film showed less frame and image embossing than the nitrate. In addition to experimental tests, the new film has been carefully watched through limited commercial trade use (theatres) for which special prints of several feature pictures were circulated through film exchanges in different parts of the country. In these tests, for which alternate reels of safety and nitrate film were used in each print, satisfactory quality was obtained in every respect. Mention has been made of the fact that ease of solubility in a large number of organic solvents was sacrificed in order to preserve the inherently good properties of the high acetyl acetate base. Thus, the splicing of the new safety film required special attention. Entirely new cements had to be manufactured and distributed. Many old types of safety film cement and previously used nitrate cements ivill not make satisfactory splices with the new base. Fortunately, the new cements, * "A Standard 0.943 Intermittent Sprocket," by Henry B. Sellwood ; IP for May 1947, p. 5. used for the new base, make satisfactory splices with the older types of safety films and with nitrate. One may therefore use the new safety cement for all films, or one may continue to use nitrate film cements for those films known to be on nitrate stock. Occasional splicing troubles arise in the use of either nitrate or safety films in which weak bonding of the film is obtained. At such times it should be emphasized that the mechanical scraping of the emulsion surface preparatory to splicing is equally as important as the cement employed. It is necessary not only that the emulsion layer be completely removed but also the very thin bonding, or sub-layer, as well. The perfectly scraped film will appear rough and dull — not smooth and shiny. It is essential that the scraper blade be sharp ! The blade should be changed whenever it fails to scrape cleanly with light pressure. With heavy usage it may be necessary to change the blade daily. Summary of Characteristics Summing up the over-all results obtained from both laboratory tests and experience in the field, the new Eastman safety film may be characterized as follows : 1. Low shrinkage will keep the film free from "buckle" and the resulting in-andout of focus images on the motion picture screen. 2. Tensile strength, rigidity, and flexibility are more like nitrate film than earlier safety films. 3. Greater resistance to effects of moisture and humidity means less processing trouble as well as less film distortion. 4. Projection quality, which is better than earlier safety films, is equal to nitrate film is screen steadiness and appearance. Projection Factors of New Acetate Film THREE factors of prime importance to the projectionist are emphasized in the accompanying candid description of Eastman's new acetate film by Dr. Charles R. Fordyce. These are: the new film's greater resistance to buckling as compared with the present nitrate stock, the reliance placed on the new standard 0.943-inch sprocket to compensate for the improved shrinkage characteristics of the new stock, and, on the debit side, the apparently well-founded opinion among projectionists generally that the new film does not match nitrate stock in tear strength. Another non-technical aspect of the situation is that the new film will cost more than does nitrate stock, the full import of which fact is not revealed in terms of the fraction of a cent increased cost per foot of original release prints. For if the new film proves more susceptible to tearing than nitrate stock, then the print-replacement cost item may have considerable bearing on the degree of acceptance won by the new film among distributors and projectionists. Tearing Strength Controls Life Much is made of the fact that the new film is more resistant to normal wear than is nitrate stock; but IP regards this as a relatively minor factor in the commercial handling of theatre film. All prints, irrespective of type, will wear out through repeated use and will exhibit a tendency to tear at the corners of the sprocket perforations. Once the perforations begin INTERNATIONAL PROJECTIONIST June 1948