Theatre Catalog (1954-55)

eS COLOR RESPONSE SPECULAR SILVER ———— SPECULAR ALUMINUM ——-—— ALUMINUM FLAKE 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740 760 WAVELENGTH (MILLIMICRONS) per cent of this energy to reach the eye. Consequently, a reflecting surface must be utilized wherein at least part of this 75 per cent loss is compensated for by a, high efficiency reflector. In this regard, it may be pointed out that a compromise exists between the so-called polarization defect and screen brightness. Obviously, if the defect or light leakage is too severe, eye strain and a feeling of general discomfort will result after being exposed to such a condition. On the other hand, if the screen brightness falls below the minimum accepted value at any seat in the theatre, eye strain and fatigue will again result. Therefore, the best allpurpose screen is one which most effectively preserves the polarization characteristics while returning to the audience the highest amount of projected energy. Benefits Derived from Lenticular Design The development of the Astrolite surface historically took place in two steps, As a basis for the optimum control and utilization of the available energy, many possible designs for the lenticles were studied until one particular pattern was evolved which gave extremely promising results. Screens manufactured with this pattern were trademarked as Magniglow surfaces, since they had the capacity to reject unwanted light and produced sharp borders within which the viewer had to be located in order to see the image on the entire screen. In order to decrease the sharpness of the borders of the field of view for indoor presentations, a special controlled diffusion process was applied to the Magniglow surface. This product resulted in what is now called the Astrolite screen. So it is seen that the Astrolite surface ig actually a combination of two processes and to clarify the structure of the component parts, 268 the Magniglow characteristics first will be discussed and then the combination of the two theories will be presented. Benefits of Lenticular Surface Among the benefits derived from the use of a lenticular surface are the following features: 1. Optimum Return of Energy—It is only with a lenticular pattern that a mirror-like reflecting surface can be used without danger of “hot spots” being produced, These brightness variations result from uncontrolled reflection surfaces wherein the incident energy is not properly spread over a predetermined viewing field. The question of the use of any particular type of metal depends, in part, upon the color response of this metal over the visible wave length region extending from 400 to 750 millimicrons. Silver or aluminum prepared by a vacuum plating process yield the highest reflectivity of any of the common metals while maintaining a uniform spectral sensitivity. This, however, does not imply that these same metals, when deposited on a supporting surface by other means, such as by spraying or roll coating aluminum flake, will give the same characteristics. With a flake mixed in a plastic carrier, there are unavoidable interstices between particles which become sources of light absorption in addition to the manifestation of color differences, Figure 1 illustrates the comparison of surface brightness between a vacuum plated, non-embossed aluminum sample and an aluminum surface which has been coated with a flake suspended in a plastic carrier, These curves clearly depict the differences which exist between specular and diffused reflection. The next series of curves taken on a Beckman Quartz Spectrophotometer illustrate the color response of a vacuum plated silver, aluminum and a flake type aluminum surface. In order FIGURE 2 is a diagram which illustrates the color response of various reflecting surfaces. to interpret these curves, the relative percentage of reflection is not as important as the flatness of the line in the 450 to 750 millimicron range of wave lengths. The more regular and flat slopes indicate a color reflectivity which is uniform throughout the color spectrum, this condition, of course, being most desirable for the projection of Technicolor pictures, : 2. Control of Fields—Another basic difference between the Maniglow screen, which has a high specular reflectance, and a diffusing type screen lies in the fact that a Magniglow screen has controlled fields of observation. By this term is meant the solid angle subtended at a point’ on the screen surface, yielding a rectangular volume. of space inside of which the image is perceived. The resulting reflecting energy under such conditions is returned in a volume of space and thus is concentrated where it can serve a useful purpose. All reflection into undesired areas is therefore eliminated, thus yielding a more efficient screen surface. Since the volume of space into which the returned energy is beamed may be controlled by the optical design of the screen surface, the image for a given projector intensity may be regulated as to brightness by the volume of space into which the image is maintained. In this connection it is well to emphasize the fact that brightness measurements made on this screen must be carried out over the entire viewing area, instead of as in the case of the diffusion type screen measuring brightness on the axis of reflection. 3. Uniformity of Field of Observation—Another basic difference between uncontrolled diffusion type screens and the Magniglow screen is the uniformity of brilliance over the useable viewing angle. It is well-known that diffusion type screens possess maximum brilliance on the axis of projection and then drop off rapidly in intensity when the viewer exceeds plus or minus 20 degrees in the lateral direction. An optically controlled surface such as the Magniglow screen reflects energy into a volume of space in a uniform manner such that the screen brilliance maintains a uniform quality to the edge of the desired field. This condition exists both in the lateral and vertical directions so that the entire viewing area receives the same brightness value, 4. Resolving Power of the Screen— Assuming that the normal eye can resolye two images separated by a given distance from the observer, the Magniglow screen possesses in its design a fusion principle wherein all the optical elements appear to be combined to the viewer’s eye and thus form a continuous imaging surface. Depending on the use to which this screen is placed the resolution factor of the size of the optical elements may be varied to yield a measure of control of screen brightness. 5. Ambient Light Characteristics — As a result of maintaining fixed boundaries for the field of observation such screens will resist ambient light inci THEATRE CATALOG 1954-55