Moving Picture Age (Jan-Dec 1922)

April, 1922 MOVING PICTURE AGE 19 one phase of the problem of projection considered in the recent studies of the Kodak Research Laboratory. Nearly all the projection screens on the market were examined, and such wide differences between the many types were found that the results are being published to help in choosing the proper screen for each particular theatre or hall. These results, of particular interest to theatre owners and managers, will also interest the non-theatrical worker who aspires to the best work. At any rate, it is now possible to select the best screen for a given theatre or auditorium with scientific accuracy, and too much attention cannot be paid to the screen. Every projection screen has its own reflection characteristics. Some reflect nearly all the light in a narrow beam, giving plenty of light for persons sitting in the center of the theatre and almost none for those at the sides. There are other screens that appear of nearly equal brightness from any seat in the theatre or auditorium. These represent extreme cases, with the majority of screens occupying an intermediate position between the two. The choice of screen depends mainly upon the shape of the exhibition room. However, in order to determine the best screen for a given theatre or auditorium, it is first necessary to determine accurately the reflecting power of the screens for all angles of view. This the Research Laboratory has done for a number of commercial screens. Orders for samples of projection screens were placed with practically every maker whose advertisement could be located in the trade journals. A response was not obtained from all the makers, but a fairly representative group of samples was received. A special apparatus, called a gonio-photometer, was constructed for the purpose of measuring the reflecting power. A beam TABLE I No. Name of Screen Manufacturer 1 .Superlite C. S. Wertsner & Son, 211-221 N. 13th St., Philadelphia, Pa. 2 Special 3 Green Back. . . . -. 4 White Back 5 Plain White Coated 6 Imsco Silver No. 1 Independent Movie Supply Co., 729 7th Ave., New York City 7 Imsco Gold No. 1 8 Imsco No. 2 9 Imsco No. 3 10 Imsco No. 4 11 Imsco White Muslin 12 Idealite — Grade 1A Ludcke Picture Screen Co., St. Peter, Minn. 13 Idealite— Grade IB 14 Idealite — Grade 2 IS. .... . Dalite Crystal White Da-Lite Screen & Scenic Co., 922 W. Monroe St., Chicago, 111. 16 Dalite Gold Fiber 17 Dalite Silver 18 Gold King Gold King Moving Picture Screen Company, 327 East California St., Oklahoma City, Okla. 19 Half-tone Raven Screen Company, 257 So. 2nd Ave., Mt. Vernon, N. Y. 20 Aluminum Paper W. G. Preddy, 187 Golden Gate Ave., San Francisco, Calif. Safety-Standard and Pathescope Films of light was thrown upon the sample of screen perpendicularly, thus illuminating it in very much the same manner as in the motionpicture theatre. A small instrument which could be set to view the screen from any angle was used to measure the reflecting power. In this way the reflecting power of the screen could be determined when viewed perpendicularly or at angles of 5 to 70 degrees from the perpendicular. These values are given for each of the examined screens in Table IV, reproduced herewith. This table contains all the necessary data for the complete specification of the reflection characteristics of a projection screen. Since we are interested in having the screen appear of satisfactory brightness to persons at the side of the theatre as well as in the center, it is necessary to decide on the maximum amount that the reflecting power can fall off before the screen brightness becomes insufficient. Making use of all the existing data on the subject, the laboratory staff decided that the reflecting power for the persons sitting at the side of the theatre or auditorium should never be less than one-fourth of the reflecting power for the persons in the center of the theatre. That is, with the proper screen brightness for persons in the center of the theatre, the brightness of the screen as seen by persons at the side should never be less than one-fourth of the proper amount. If the ratio of the reflecting powers is greater than four to one, it will result in diminishing the number of good seats in the theatre or auditorium. Obviously, a screen that would give excellent results in a ; long, narrow hall might not be suitable in a very wide hall where the angle of view is greater. The maximum angle of view can be determined from a floor plan of the hall. It may be found by drawing a line connecting the most extreme seat on the side with the center of the screen. The angle of view is then measured between this line and a line drawn through the center of the theatre. It will sometimes be found that there are a few seats on the side that will add to the angle of the theatre or auditorium considerably. If these seats are usually vacant, it may be undesirable to increase the angle for the benefit of the few persons who might occupy them. The accompanying floor plan of a theatre or auditorium illustrates this point. The required angle, counting all seats, is 40 degrees. However, 95 per cent of the seats are contained within an angle of 30 degrees. With the knowledge that these seats will not be as good it is sometimes permissible to choose an angle that does not include them. The distortion, which no ordinary screen can correct, is often more annoying from the side seats than the loss of brightness. TABLE II No. See able I Maximum Angle Average Reflecting Power Color Texture 6 20° 218 Metallic White Coarse Grain 18 20° 209 Metallic Yellow Smooth 1 20° 205 Metallic White Coarse Grain 2 30° 204 Metallic White Coarse Grain 7 30° 184 Metallic Yellow Coarse Grain 8 30° 165 Metallic White Coarse Grain 9 30° 150 Metallic White Medium Grain 17 30° 128 Metallic White Fine Grain 20 30° 96 Metallic White Smooth 3 40° 136 Metallic White Fine Grain 10 40° 129 Metallic White Fine Grain 4 40° 121 Metallic White Fine Grain 13 50° 104 Metallic White Medium Grain 16 50° 79 Metallic Yellow Fine Grain 12 70° 92 Metallic White Fine Grain 14 70° 89 Metallic White Fine Grain 19 70° 70 White Smooth 5 70° 69 Yellow Smooth 15 70° 68 Blue Green Smooth 11 70° 62 White Smooth