| 摘要 |
PROBLEM TO BE SOLVED: To restrict visibility of video information by eliminating the nonuniformity of brightness within a screen, and uniformizing the brightness of an entire screen within a suitable range for viewing and on the other hand making the entire screen dark on the outside of the suitable range for viewing. SOLUTION: A transmission type screen 9 is constitute of a Fresnel lens 9a condensing video light from a projection lens at a specified focal distance (O point) and a lenticular lens 9b having angle-of-visibility characteristic to quickly attenuate the spread of incident light by angles of visibilityθ1 andθ2. Thus, a large difference in contrast is made between the inside and the outside of the suitable range for viewing, so that the suitable range for viewing is defined and uniform brightness is simultaneously obtained over the entire screen within the suitable range for viewing. Also, the brightness is made extremely low on the outside of the suitable range for viewing, from which it is in possible at all to obtain the video information.
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