International projectionist (Jan-Dec 1939)

Color Film Screen Values1 By W. C. HARCUS TECHNICOLOR M. P. CORP.. HOLLYWOOD, CALIF. The color intensity of a motion picture projection system may affect the presentation of the picture. Using sample comparison methods the average color of projection systems can be determined ami the deviation of a particular system measured. CONSIDERABLE data have been collected and published concerning motion picture screen illumination from the standpoint of intensity. There is very little information concerning the color of projection systems. A projection system includes the light-source, optical system, and screen. The color of the light-source may vary from the yellow of a "Mazda" lamp to the bluewhite of a high-intensity arc. The quality and condition of the elements of the optical system will affect the color of the light leaving the projector. The color of the light reflected from the screen will be affected by its type and condition. A rapid and simple comparison method of determining the color of the system by measurement of the light reflected from the screen has been developed. The equipment used consists essentially of a light-source of adjustable color and intensity and a powersupply unit. The variable light-source consists of a slide-film projector unit equipped with a 500-watt "Mazda" lamp, a lens with iris diaphragm, and a filter holder mounted in front of the lens. The power-supply unit consists of an autotransformer with an output range up to 130 volts when supplied with 115-volt, a-c power. A voltmeter and ammeter are wired into the unit which also serves as a support for the projector. Auxiliary equipment includes a set of "Daylight Blue" filters ranging in thickness from 0.04 to 0.10 inch in steps of 0.01 inch, a white "standard screen," and a set of colored reflection screens. The technic of making a screen-color measurement with the "comparator" is essentially as follows: • Measurement Procedure (1) Set up the standard screen as near the center of the projection screen as practicable. (2) Set up the comparator in front of the screen and adjust the beam so that it just covers standard screen. (3) Operate the projector system, and erect a mask to shield a small standard screen from the light-beam. (4) Insert a suitable filter in the comparator and adjust the intensity to match that of the projector system. tJ. Soc. Mot. Pict. Eng. (XXXIII) Oct. 1939. (5) Refine the color match between the standard screen and the screen being measured by adjustment of the filters, and record the filter thickness. (6) An alternative method employs tinted screens instead of a whitescreen-and-filter combination. The procedure is essentially the same. Interpretation of the results of comparative measurements may be in arbitrary units, such as filter thickness, which in turn may be translated into other units as desired. • Wide Projection Range A number of measurements have been made with the comparator in East and West Coast theatres, and in many of the Hollywood studios. Analysis of the data indicates that there is appreciable variation in color of projection systems. The average system color may be reproduced with a 0.13inch "Daylight Blue" filter in the comparator; deviations of ±0.03 inch in thickness from the 0.13 average are found. DISCUSSION Mr. Crabtree: How does this variation in color affect audience reaction? That is the only way we can estimate the importance or seriousness of this variation in screen color. Have you made any audience tests? Mr. Harcus: Not in the sense in which you are thinking, I believe. In viewing a picture on the screen, whether black-and-white or colored, the viewer, unless the color deviation is very marked, may not notice the difference in terms of neutral gray in the case of black-and-white, or the color variation in the case of a colored picture. If the deviation is very marked the difference becomes very objectionable. Mr. Hooper: What kind of instrument do you use to determine the color of the light on the screen in case you want to get any particular color? Mr. Harcus: We are using this type Old Book Wanted A subscriber to I. P. is very anxious to obtain a copy of "Electricity for the Motion Picture Operator," published in 1922 by Cameron Publishing Co. and now out of print. Anybody having a copy of this book for sale should communicate with I. P. of comparison unit with which the color of the screen is matched, as demonstrated. Mr. Hooper: Do you have any instrument with which to measure the color-temperature of the light on the screen? Mr. Harcus: We have not yet undertaken any studies to that extent. Mr. Carlson: Does the range of color difference shown here represent an acceptable range? Do you have any means of measuring screen brightness rather than incident light? In several instances where a balance presumably was demonstrated, differences in brightness seemed to be apparent. Was that due possibly to the fact that the photocell is not color-corrected and due to the selective reflectivity of the screen itself? Mr. Harcus: There is the degree of difference we have observed here. I believe this represents a greater deviation than is desirable for the presentation of either black-and-white or colored pictures. The meter we use for this type of work is a simple Weston meter. This is a photoelectric type of meter and measures the light falling on the screen. It is not accurately color corrected so far as color-sensitivity of the eye is concerned. Mr. Kellogg: I take it from your answer to Mr. Crabtree's question that the audience is not very critical of the color and that if the color source did vary over a certain range the audience would not criticize it. If that is the case, I do not quite see the purpose of making this rather exact study. For color projection do you find a still greater premium on very high screen brightness than you need for black-and-white pictures and do you get more return psychologically from high brightness in the case of color than you do black-and-white? Ten ft.-candles 'Average' Screen Mr. Harcus: The purpose of the initial investigation was to determine the average screen color of the many theatres we encounter. This was to be determined as a control for the manufacture of color pictures. Color pictures that look the best on the "average screen" may not look quite so good on screens that deviate from the average. We find in terms of light falling on the screen, that the average large motion picture screen does not exceed 10 foot-candles by any substantial amount. We have found some running as high as 13 and a few as high as 18 or 20. We have found some as low as 5 foot-candles at the center of the screen. We manufacture color pictures to show to the best advantage on an average screen of 10 footcandles. Mr. Richardson: In lighting for color photography we have a problem quite similar to the one here under consideration. The requirements of color photography rather closely limit the spectral quality of the sources used on the motion picture set. Until we devised a (Continued on page 25) 16 INTERNATIONAL PROJECTIONIST