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1954-55 Theatre Catalog, 12th Edition, Page 307 (271)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 307
Page 307

1954-55 Theatre Catalog, 12th Edition, Page 307

FIGURE 9 is a lopoaruphical map illustrating flow pattern of the Magniglow screen design.

an angular separation of 70 Seconds between distant objects, If the adjacent images formed by the mirrors exceed this separation for a given viewing distance, then each individual image will be seen and the projected image texture will lack definition.

Returning to a study of Figure 6, the blending of images is not arranged in an optimum manner, since the lateral image displacement is greater than the vertical separation between consecutive images. 7

To counteract this defect, the elements may be staggered with images appearing as shown in Figure 7. The resolution is improved with this arrangement of elements; however, there becomes evident another defethhat of sharp discontinuities in the flow pattern. Performing an embossing operation on such a pattern results in structural weaknesses and uncontrolled areas of stray refiectivity.

Another possible screen design would incorporate alternate concave and convex surfaces in an attempt .to reduce ttdead space/i i.e. space on the screen surface which does not possess controlled convolutions. As is seen from Figure 8, the area marked its" may be considered "dead space" if no attempt is made to How the pattern from element to element. If an attempt is made to blend the curves, a saddle pattern results which of necessity will have different fields of observation than will the computed alternate concaves and convexes.

Controis Entire Surface

The design which controls the entire surface of the screen with none of the defects mentioned above will now be the topic of discussion. This screen has a designed lateral angle of 100 degrees and a vertical angle of 50 degrees. For any other field of observation, the shape of the pattern will change but the basic dow characteristics will remain unchanged. The size of the largest element was selected after consideration was given to the resolving power of the eye and the relative motion of the images.

The topographical map of Figure 9 illustrates the flow pattern of the Magniglow screen. Solid lines on this map denote the curvatures which occur when progressing in any direction. The dotted lines portray the field stops for the

FIGURE 10 is an illustration of the manner in which the controlled diffusion is accomplished.


various elements. A second view of these elements with the appropriate stops show that in the vertical direction, each element has a diameter of 0.0208 inch. The horizontal diameters vary from 0.008 to 0.0166 inch, to compensate for varying radii. If a vertical line such as that represented by BOB in the drawing is selected, it is noticed that the elements alternate in curvature along this plane so that a convex, concave, convex pattern is maintained. The elements located at right angles to this plane such as those located at ABA and DCD determine the horizontal field and are all concave in nature while the adjacent row of elements are all convex. As a result of these curvatures, the vertical field of observation is maintained by alternating convex and concave elements while the horizontal field is composed of vertical rows of concave elements adjacent on either side to vertical rows of convex elements.

The last observation to make with reference to the topographical drawing is that of the various surface levels of the elements. It is for this reason that the sagitta or arc depths are of importance. So that no part of the surface is left undesigned. the depths of a curve in one direction must be adjusted to

meet the depths of the curve running at right angles to it and at the same time retain the field of view desired. Thus, the figure shows reference levels labeled A to D corresponding to the elevation levels of the various elements.

Controlled Diffusion Type Surface

The physical environment of the indoor theatre necessitated a reflective surface whose basic properties consisted of those described above and in addition, a mellowness and uniform drop-off in brightness at the borders of the field of observation. A fully specular, lenticular screen would give uniform light distribution and would serve well to restrict viewing angles. However, since there is no way to predetermine the most desirable viewing area for all theatres, an arrangement of controlled light distribution was developed whereby under any existing condition the field uniformity could be preserved. The method of performing this function consists of coating the refiective surface of the screen with a plastic containing minute granules of a diffusing agent. These particles may be, for example, glass, silicon dioxide powder, or any material which when projected upon will cause a light scattering to take
1954-55 Theatre Catalog, 12th Edition, Page 307