Motion Picture Herald (Oct-Dec 1951)

VISION RANGE The field of view relative to the screen of an audience in a motion picture theatre is diagrammed at left for various viewing distances in a drawing by Sylvester K. Guth of General Electric, developed from studies which he reported to the Society of Motion Picture & Television Engineers (SMPTE Journal, September, 1951). The areas of vision occupied by the screen are indicated by rectangles at the center (see text below). inated picture cannot be properly enjoyed because of the visual fatigue caused by the sharp contrast and the glare produced by the black masking, with the result that the greatest contrasts occur at the edges of the picture, thus reducing the sensitivity of the eye to the detail in the picture. Many attempts have been made to project a luminous frame surrounding the picture from a separate light source. These e.xperiments show that any reduction in contrast between the surround and the picture is desirable. However, fixed intensity light surrounds still give the effect of a limiting picture frame. SURROUND LIGHTING METHODS There are now two methods of synchronous screen surround illumination which utilize the film projection light source modified by the density and hue of the film passing through the projector aperture. T'he system used in the Telekinema of the Festival of Britain had a lens and mirror assembly in conjunction with the projector, which required care and cleaning of these optical parts. Screen surround construction is also necessary that can receive the light projected through this optical system. The system developed in this country and recently installed in the Plaza at Scarsdale, N. Y., and the Cinema at Framingham, Mass., utilizes only a specially design screen frame construction, and reflecting materials to surround the picture rvith a synchronous bath of light, d'his system has the advantage of low cost of installation and no operating cost whatever. It can be manufactured as a prefabricated “package” for convenient adaptation to existing theatres. It is desirable to have the screen surround illumination, at any given point. related in intensity and hue to the immediately adjacent picture area. This is achieved to a greater extent in the American examples because the main source of light for any portion of the surround is derived from screen light reflection at the contiguous picture area. (The British system claims that the color content of the transmitted light is de-focused or diffused to give a uniform color. ) To the extent that the synchronous light surround matches the adjacent picture area, the viewer is more able to imagine the picture area blending into the surround lighting, with a resultant heightening of the sense of realism. A very large area of auditorium wall and ceiling surfaces is visible from the average viewing position. Mr. Guth’s accompanying diagram (shown above) illustrates this effectively. The three rectangles at the center of the diagram, marked A, B and C, show the total field of view of a pair of human eyes that is occupied by a motion picture screen, at viewing distances amounting to the width of the screen (IW), three times the width (3W) and five times the width (5W). The shaded portion of the diagram indicates the field of view of one eye only. WHAT THE EYES CAN SEE Now In Figures 1 and 2 Is shown the amount of the field of view occupied by the walls and ceiling of an auditorium. The extreme viewing distance is shown at 5W on these diagrams, and this ratio is recommended as the maximum for determining picture size. Mr. Guth’s diagram shows very effectively how insignificant a portion of the field of view the picture occupies at 5W. It is advisable to use a picture size as close to 4W as the seating arrange ment nearest the screen will permit, provided that sufficient screen illumination is maintained. Figures 1 and 2 show that more of the walls and ceiling of a theatre come into the critical portion of the field of view as the room becomes narrower and lower in height. Note in the plan view {Figure 1 ) the amount of wall area which comes within the normal two-eye field of view, which is 120° horizontally. Figure 2 shows the amount of ceiling visible in the vertical field, which is 60° above the horizontal. Figure 1 also indicates wall areas which come within a horizontal viewing angle of 60°. It is within this smaller angle of view that greatest care must be taken as to the surface visible within this range. Similarly, in Figure 2, the surfaces of the ceiling seen within the vertical viewing angle of 30° above the horizontal require great care in treatment. Specifically, the surfaces from points A to H , or A to D, in Figure 1, and the ceiling from points A to D, or A to F, in Figure 2, are the surfaces coming within the critical viewing zone. In these critical areas we find the screen, the immediate screen surround, and what may be termed the transitional areas blending the screen surround to the remainder of the auditorium surfaces. TREATMENT OF SURFACES The next surfaces to consider are those which occur just beyond the aforementioned zones and are contained within the 120° horizontal and 60° vertical viewing angles in Figures 1 and 2. In existing theatres, these latter surfaces may be effectively treated by proper painting, with color and finish as hereinafter recommended. Beyond the above areas, the walls and ceiling can be treated decoratively in an optional manner, and here secondary (non-screen) light sources may be used to advantage. It is to be noted that no secondary light sources should be used to light the visible surfaces in the critical areas nearest to the screen. Figures 3 and 4 illustrate the behavior of light as reflected from the screen on the auditorium surfaces. Figure 3 shows two types of broken surfaces which would normally contain a shaded and shadow portion due to the location of the screen light and the break in the surface. Note the portion ‘^Af’ which is recommended as a filler section to create screen light reflection where a shadow would otherwise exist. These alterations need be made only on those surfaces which come within the 60° horizontal viewing and the 30° upward viewing angles. Figure 4 shows how screen light is reflected on the side walls and re-reflected {Continued on page 26) 12 MOTION PICTURE HERALD, DECEMBER I, 1951