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OGEE LENS FREE MIRROR FREE DIA.= 24
50 60 70
DISTANCE FROM PRIN. FOCUS TO SCREEN
Fig. 3. This illustrates range of projection distances available with the 15.515-in. focal length Ultra-Speed System by use of ogee lenses designed for ideal projection distances of 55.3 ft and 71.6 ft. It also illustrates range of picture sizes available by varying kinescope raster diagonal between 5.31 in. and 7.0 in. Curves of constant illumination indicate available range of screen illumination levels, based on a level of 100% at 62 ft from a 6.25-in. diagonal raster. This level is about 2 ft-c in the highlights with currently available kinescopes.
system will produce pictures at lower illumination levels because the pictures are larger. This can be controlled to a limited extent by electrically varying the raster dimensions in inverse relation to the throw. An increase in throw will then be attended by a decrease in raster area. But, since the beam power is not reduced, the raster brightness increases. By this means, pictures can be kept at approximately constant size and brightness over a considerable range of projection distances. For example, it is seen from Fig. 3 that the projection distance can be varied between 57 ft and 67.6 ft with no change in picture size and with an illumination variation of only 1 0% from the average. Also, picture widths can be
varied between 17.2 ft and 22 ft with no change in projection distance and only a 10% illumination variation from the average. When the ogee lens is changed, and a new range of projection distances is entered, the choice of picture brightnesses and sizes available with the particular lens is, of course, altered. In order to have the above-described ranges of projection distance and picture size available with a single ogee lens, the lens would have to be designed for an ideal working distance of about 63 ft. The ogee lenses used with this system are presently being made for an ideal projection distance of 62 ft. Future installation requirements will determine the choice of additional lenses.
Sachtleben and Alice: Theater Television Optics
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