International projectionist (Jan-Dec 1950)

SMPTE Screen Brightness Survey THE wide variance in screen brightness levels in motion picture theaters throughout the country has spurred the Society of Motion Picture & Television Engineers to throw into action its Screen Brightness Committee which did such a fine exploratory job on this problem in the early part of 1948. At that time the Committee was hampered by the lack of a suitable meter for the measurement of screen illumination and screen brightness— a distinction of terminology which alert projectionists should keep in mind. This deficiency in suitable measuring instruments has now been largely overcome through the cooperation of General Electric Co., which has generously made available to the Committee a specially designed meter which should meet FIG. 1. DATA SHEET FOR DETERMINING SCREEN ILLUMINATION BY THE 5-POINT METHOD Read intensity on the screen in foot-candles at the five positions indicated. G and C2 are located 1/20 of H from the edges and 1/20 of W from the sides. Bi and Be are on the horizontal center and 1/20 of W from the sides. A is in the exact center. SCREEN AREA AREA IN SQUARE FEET =ff X W= 0) SCREEN LIGHT INTENSITY AND DISTRIBUTION RATIO 2 C,*Ci SCREEN LUMEN CALCULATION A X 2 = B,*B£ = C,*Cg _ 2 TOTAL = WEIGHTED AVG.= T°JAL = SCREEN LUMENS = (l)x (2) = (2) all requirements for a genuinely scientific approach to this vexing problem. Within a few weeks members of the Screen Brightness Committee will visit a representative number of theaters throughout America for the purpose of gathering data which, when correlated, should serve as a firm basis for estimating current field practice in terms of acceptable screen brightness. IP solicits the utmost cooperation of projectionists to the end that this survey shall be productive of results which will aid the motion picture industry over-all, let alone the projection field. (See "In the Spotlight" department on page 16 of this issue.) 1948 Survey Results Discouraging In 1948 conditions nation-wide ala screen brightness levels were anything but encouraging to those who regard projection as the bottleneck of all industry effort to deliver to theater screens the finest pictorial image possible. True, the number of theaters surveyed two years ago was limited, but they were of such variety as to occasion grave doubts among technicians that the exhibition field was making a sincere effort to improve the quality of the projected image and thus aid the box-office, the source of income for the entire industry. For example: an analysis of the 1948 survey data disclosed that only 50% of the theaters had a screen brightness level approximating the recommended range of from 9 to 14 foot-lamberts. Of special significance was the fact that only 12.5% (or 1 out of every 7) projectors checked were capable of delivering the recommended screen brightness level. Total lumens on the screen and lightintensity distribution over-all from center to sides of screens (the only honest evaluation of projection quabty, as pointed out repeatedly by IP) varied from a minimum of 7 to a maximum of 30 footcandles. Approximately 50% of the projectors gave from 10.5 to 1 6.5 footcandles. An analysis of the distribution of light intensity showed that two-thirds of the projectors provided from 50 to 75% as much light at the sides as at the center of the screen. Two projectors provided only one-third as much light at the sides as at the center — glaring examples of misadjustment of equipment. Figures on Screen Lumens Generally, the survey showed that the screen lumens obtained fell below the expected values. About 17%% of the projectors obtained all the light to be expected from their equipment. On the other end of the scale, 7.5% (woefully low) were obtaining only from 35 to 45% of the light estimated to be obtainable. About 50% of the cases surveyed resulted in a range of from 35 to 75%, which figures, while by no means representing PROJECTION DATA: 1. Projection Angle 2. Arc Lamp Type 3. Positive Carbon 4. Negative Carbon , 5. Arc Amperes 6. Arc Volts : . 7. Projection Lens (a) f/ Number (b) Focal Length . . . (c) Surface Coated Yes — No 8. Type of Shutter (a) Degree Opening .... . 9. Draft Glass Type . 10. Heat Filter Type 11. Projection Port Glass... Yes — No 12. Type of Power Supply . . . (a) Rating in Amperes . . (b) Rating in Volts (c) Operating Voltage . . . AUDITORIUM DATA: 1. Seating Capacity good performance, represented all the light obtainable from the equipment. The over-all results of the 1948 survey clearly indicated the pressing necessity for an extended survey of a greater number and more varied types of theaters as a requisite preliminary to an all-out effort to raise the general level of screen brightness. This project will now be undertaken by the Screen Brightness Committee. The results obtained in the 1948 survey were representative of theaters having screens in the range from 12 to 31 feet wide, with seating capacities from 300 to 6200 seats, and with projection "throws" from 65 to 207 feet at angles from 5 to 24 degrees. It is not known at present whether (Continued on page 23) FIG. 2. SHOWING LOCATION OF AUDITORIUM SEATING POSITIONS FOR BRIGHTNESS MEASUREMENT POSITIONS: (1) Center, 3Vi screen widths back from the screen (2) Left front corner seat (3) First row center (4) Balcony top row center Read brightness at 3 places on the screen from auditorium positions 1, 2 and 3, but only the center from position 4. 10 INTERNATIONAL PROJECTIONIST July 1950