The motion picture projectionist (Nov 1931-Jan 1933)

November, 1931 Motion Picture Projectionist 33 Report of the Screens Committee The report which follows presents the findings of the Projection Screen Committee of the S. M. P. E. The Committee is composed of S. K. Wolf, Chairman, and the following members: D. S. De Amicis, F. M. Falge, H. Griffin, W. F. Little, A. L. Raven, C. Tuttle and D. F. Whiting.— Tuts, Editor. ' I VHE Projection Screens Committee commenced its operations in March. The first meeting was held on April 16th in New York, N. Y., at which the Chairman submitted a preliminary outline of the work proposed for the Committee to undertake. This outline was discussed and elaborated and as a result a second and more detailed outline was prepared and distributed among the members. The second meeting was held on May 14th. This preliminary report is based largely on material submitted and examined at that time. The main lines of endeavor are outlined as follows: Manufacture of Screens, Mechanics, Light Reflection Properties, Sound Transmission, Illumination, and Rear Projection Screens. Responsibility for the different sections has been assumed by the members with regard to their familiarity with the different fields. Considerable data will be collected on light reflection properties, brightness values of screens in theatres, and manufacture, installation, and maintenance of screens. It is also hoped that the Committee will be able to make recommendations as to the type of screen to employ under specified conditions of use. The following is in the nature of a preliminary report and, therefore, is not as complete and conclusive as we should like it to be. Nevertheless, it is our opinion that it offers material which the Society may find of interest at the present time and will indicate what may be looked for in our later report. Bases. — The manufacture of sound screens is a critical undertaking in which all details must be given due consideration in order that uniformity and high quality of finished product may result. Most screens employ a fabric as a base although there are some which employ a metal. Essentially, the. purpose of the fabric is to provide the necessary strength for the screen and to serve as a carrier for the light reflecting surface. Quite often the fabric is coated with a cellulose compound and the combination employed as a base. With some screens a slight translucency of the fiber from which the fabric is woven is desired. This is the case when the rear surface of the screen is colored in an attempt to impart to the reflected light a slight tone of the particular color used. It is more customary, however, to make the fabric as nearly white and opaque as possible in order to improve its light reflecting qualities. Surface Treatment. — The base fabrics are treated in various ways to give various reflection characteristics to the screens. The surfaces are classified as matte or diffusing, beaded, or metallic, the latter two being somewhat directional in their distribution of illumination. They may be applied by a knife spreader process, by printing with rollers, or by spraying or painting. Great care must be taken to secure a uniform and sufficient thickness of coating to provide good light reflection characteristics while staying within the limits imposed by other conditions. As yet, no detailed information has been collected in regard to the materials which are commonly used for surfacing. It is present practice to color the backs of screens for purposes of identification. As mentioned before, however, color is sometimes used with thin surface layers to provide a slightly selective reflection characteristic. Materials for coating vary srreatly in their properties. Some diffusing screens are slightly glossy and others have perfectly flat white surfaces. Flat white seems best for avoiding surface glare and undesirable reflection at the seams. Diffusing surfaces may be hard or soft, smooth of rough. A hard smooth surface without sheen is apparently desirable since it is less apt to collect dirt and is easier to clean. Beaded screens require ingredients to hold the beads firmly in place. Most surfaces are formed from pigments and gums, oils, or other binders. In general, the gums and oils cause screens to become yellow with age. Fireproofing. — At various times •there has been agitation in regard to fireproofing of screens. This situation grew out of the practice of using highly inflammable nitrocellulose bases. Screens of this type are undoubtedly fire hazards and their use has been largely discontinued. At present, practically all screens are either slow-burning or fire-resistant. They are made so by properly selecting the materials and by flameproofing the base fabric prior to treatment of the surface. This Committee has found that it is impossible successfully to fireproof a screen after manufacture or when in place in the theatre. It must be remembered that the screen is a small item in the stage equipment of a theatre, that it is usually much less inflammable than the surrounding draperies, and that usually it is hung vertically and stretched tight, so that it is not likely to be the cause of fire. We know of no case in which slow-burning or fire-resistant screens have caused fires. In general, it devolves upon the exhibitor to make his choice of screens, depending on his own local ordinances and conditions. The Committee is considering a recommendation relative to the marking of all screens which have been flameproofed so that difficulties arising in this connection may be eliminated. Sound Requirements. — After many tests, the necessary requirements as to the ratio of open to solid space in sound screens have been determined by producers of sound equipment, 40* z<f o* ao" *o~ «o' «o* ANGLE OF OBSERVATION Fig. 1. Distribution of Brightness in Horizontal Plane for Diffusing Screen ABOVE ANCLE OF OBSERVATION BELOW Fig. 2. Distribution of Brightness in Vertical Plane for Diffusing Screen