> > > >

1954-55 Theatre Catalog, 12th Edition, Page 306 (270)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 306
Page 306

1954-55 Theatre Catalog, 12th Edition, Page 306

degrees, all that; is required is to decrease the element diameter to approximately 0.40 inch as shown in the second drawing.

Obviously, it is at the disposal of the designer to select a different combination of element diameter and curvature to obtain the same Viewing field. This concept is illustrated in the third drawing of Figure 5, where the angle is 90 degrees but the radius of curvature is 0.625 inch and the element diameter is 0.53 inch, It must be remembered that when the projection beam is directed along the axis of the mirror, the image is formed on the optical axis; however, if the projection is made at

an angle to the mirrors optical axis, then the image is displaced and will produce a non-symmetry in viewing angle. As is generally the case, the projector is sufficiently distant from the screen surface so that the beam does not strike the refiector at a large angle. Of course, a viewer looking at the surface can place himself in such a position that he is out of the field for part of the screen and in this case it will be noticed that the screen appears dark due to the absence of refiected light to the observers eye.

FIGURE 8 illustrates undesirable dead space between series of concave and convex lenticles.

FIGURE 8 (top, left) shows image formation with udioining convex mirrors. Figure 7 (bottom. left) the arrangement of staggered convex elements.

Proper Selection of Lenticles

Up to this point the discussion has concerned itself with the manner in which the desired field of observation is obtained and some of the properties of curved mirrors. Now it will be shown that there are many possible combinations of mirrors which give some of the lenticular effects, with but one particular pattern possessing optimum characteristics. Let us select elements of a convex nature arranged as illustrated in Figure 6, with the projector illuminating the screen in a fashion so that the visual images are located in the center of each element; any motion of the observer will apparently cause the images to move with this Observer. Again, the curvature and diameter of the elements yield a controlled field of observation. Since the redecting surface described here is strictly specular with no diffusion entering, the primary disadvantage of utilizing this design for a Magniglow screen is that the image boundaries contain ffdead space," or space which is optically inactive. Ridges formed by the surface discontinuity at the field stop result in ffhot spots, produced for certain viewing angles. A person studying such a screen would notice that bright points of light or scintillations would occur and produce uneven light distribution.

Another consideration that must be given serious thought when possible designs are being considered is the screens resolution characteristics. It is understandable that some upper limit must be placed on the element diameter; otherwise, a screen of coarse texture would result. As a basis for selecting the optimum size of each lenticle, it is assumed that the average eye can detect

@ ,e



1954-55 Theatre Catalog, 12th Edition, Page 306