The motion picture projectionist (Nov 1931-Jan 1933)

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12 Motion Picture Projectionist The Treated Screen Surface December, 1932 HOW may conditions pertaining to every-day visual activities be improved to enable us to see without strain or fatigue? Visual activities, of individuals of all classes, of all ages, are many and varied. We know that millions, old and young, are suffering from deficient vision today. Accepted as fact, is the knowledge that our eyesight has deteriorated rapidly since the advent of the electric or artificial light. The normal vision of the human race must be conserved at any cost. Eyes, other than normal must be protected, first by proper optical aid and glasses, and then conserved by conditions of light and stimulation within limits of normal functioning. Inadequacy of Artificial Light Artificial light, improved in intensity and quality since its inception, is not yet comparable with daylight. Our eyes evolved under daylight conditions, under high intensities of light of a quality or spectral character not obtainable from the ordinary artificial light sources, which in these modern times, we must constantly employ in our daily visual activities. Organically our eyes have not changed to meet conditions of artificial illumination and the nearness of the light source. This wonderful sense organ, the eye, flexible and adaptable to almost any intensity of light of a daylight character, is now subjected, most of the time, to artificial light of relatively low intensity, lacking blue and green rays and having a preponderance of yellow and red rays. We will not say that the blue and green rays are more essential or beneficial to the eye than the yellow and *red rays. We do claim, however, that a light such as average daylight, having a continuous spectrum and composed of a relative even number of waves of radiant energy, is best for the eyes and will improve vision; also, that artificial lights with a preponderance of yellow and red rays, cause eye-strain and fatigue, are harmful to the eye and impair vision. High intensities of even two or three thousand foot candle brightness of a daylight character cause only normal reaction of the pupil of the eye, while low intensities of artificial illuminants with their preponderant red and yellow rays cause glare and pupilary contraction that should and can be controlled. Brightness of the retinal image is proportional to the diameter of the pupiliary opening which we find is involuntarily controlled by quality, as well as by the intensity of the light. The small-size pupil influences definition only at very high intensities. Keeping the pupil of the eye open to a diameter of three, instead of two millimeters, under low intensities, produces approximately the same increase of By ALBERT B. HURLEY* vision as would result from a several hundred per cent increase in illumination; The Treated Screen Surface Seeing depends upon three things namely, the light source, the surface of the object being viewed and the eye itself. We cannot change the natural reaction of our eyes to light, but much can be done to improve the light to which they must adapt themselves in the function of vision. Now, what combination of light, surface and resultant reflected light is best for the eye and will cause normal functioning, without strain and fatigue at either maximum or minimum limit adopted? The optican can keep our eyes in good condition. The physicist has given us improved artificial light and is working to perfect its quality. In working towards better vision, consideration of the surface is equally important. A new development in this direction is the practice of treating the reflecting surface such as the printed page or motion picture screen, etc., with due consideration to the incident light and the need of the human eye, so that the surface will reflect to the eye a corrected light spectrum within limits of average daylight stimulation. If the character of the surface can be selected, so much the better. This can be done in the two applications just mentioned. The base for a motion picture projection screen must be as diffusing as it is possible to obtain and within the limits of a so-called white surface. The better the dffusion the more perfect will be the vision for all persons viewing the picture. The writer has made a surface diffusely reflecting approximately 92% of the incident light, which may be considered as one measure of visual result in this particular application. Intensity of artificial lights can be controlled and better visual results can be obtained by correcting or improving the quality or spectral character. Attempts to correct the spectrum of artificial lights by filters have been successful to some extent, but the efficiency of such filters is very low. Nature has given us pigments that absorb and reflect light more efficiently than any manufactured filter absorbing and transmitting light. Therefore, the practice of using such pigments on a reflecting surface to correct the spectrum, furnishes another measure of vision, the results being in accord with type and efficiency of the light used. It becomes then only a matter of choosing the best illumination intensity of each installation of a motion picture screen employing this new method. By means of a spectrophotometer, we measure the capacity of the surface for reflecting each and every wave length in the incident light whether its source be the Tungsten Projection, the D. C. Arc or any other type of light source advocated. Knowing the radiant energy given by each of these light sources, the screen base is then treated with a selected pigment, which absorbs part and reflects part of the incident light, so that each unit of surface reflects a composite of light rays simulating average daylight. By absorbing any preponderant yellow and red rays, we accentuate the blue and green rays and make them more efficient in giving perception. Quantity vs. Quality A screen was constructed using onehalf present diffusing type material and one-half treated screen material, each side being illuminated by a D. C. Arc projector, each arc using current of 26 amps. Attempts to match the two sides, and balance the entire screen illumination by raising or lowering arc current, were influenced by color differences. However, a near match was found by using 26 amps, in projecting on the untreated screen surface and 17 amps, in projecting on the treated surface. A picture was then projected upon untreated screen and several observers noted brightness and definition characteristic of several values in arc current, with the result that 26 amps, were used to give satisfactory result. The picture was of a man seated at a desk and observers were each given some fine details to closely observe and to comment upon, such as the face and eyes, collar and tie, suit, pictures on wall, etc. On the treated screen the same picture gave satisfactory results at 15 amps. There was better definition and many details not noted before were readily visible, such as design in necktie, a mustache, and determination of subject in pictures on wall not known before. Advantages of Corrected Light Light reflected from the treated surface will normally and evenly stimulate the retina by a pre-determined period of vibratory wave lengths causing a normal functioning of all processes of the eye. This corrected light will prevent over stimulation causing the sensation to "over-shoot" its value. After-images, both positive (due to intensity) and negative (due to fatigue), will be minimized. The eye adapts itself quickly to light from a lower to a higher intensity but very slowly when subjected, first to a high and then to a low intensity. * Inventor of Orthocrome Screen. Designer of screens in Radio City. :