| 摘要 |
PURPOSE:To deviate the optical path of external light which enters a back projection video projector and to prevent the external light from being projected on a viewer side as reflected light by arranging microprism lenses which are used to direct an optical axis upward on the front sheet surface of a transmission screen in a same level with a part where an image projection beam is transmitted. CONSTITUTION:A screen is equipped with the transmission type screen 17 having prism lenses 112. An image projection light beam 14 is transmitted through the screen 17 and then its optical axis is changed upward in direction by 7 deg.. External light 108 from an electric lamp, etc., positioned at, for example, 45 deg. enters a cabinet and then the 2nd mirror 16 operates as a reflector 109, so it returns to the side of the screen 17 by reflection. The screen 17, however, incorporates the prism lenses 112, so almost all the reflected light 110 returns to the external light source side and is never projected on the same side with the image projection light beam 14.
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