| 摘要 |
PURPOSE:To attain maximum brightness in dependence upon the angle of the eye viewing the screen by arranging a Fresnel lens placed between a lentiscreen and a projecting lens so as to be movable vertically. CONSTITUTION:The image light projected by a projection tube 1 is projected by way of a projection lens 2 onto a lentiscreen 4 and the thus projected image is viewed from the side opposite to the projection surface by the projection tube 1. The Fresnel lens 3 is placed between the lentiscreesn 4 and the projection lens 2 in the rear projection television and adapted to be movable vertically. For example, when the Fresnel lens 3 is moved up, since the center C of the Fresnel lens 3 is offset from the center C' of the screen, the optical axis is offset from the projection lens 2 upwards at the center C of the screen. Therefore, the brightness becomes maximum with the viewing position of the screen 4 above the center C of the screen to increase the gain.
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