| 摘要 |
PURPOSE:To decrease hot spotting and to increase a diffusion angle by varying the microcurvature of a Fresnel lens from the curvature of the original lens to disperse the focuses of the incident light on the respective microcurved faces and using such lens as a transmission type screen. CONSTITUTION:The curvature of the microcurved faces of the Fresnel lens 64 is made larger or smaller than the curvature of the microcurved faces of the original lens (shown by a broken line in the figure) and is thereby varied. Such Fresnel lens 64 is used as the transmission type screen of a back projection type projector and the functions capable of diffusing light are provided to the respective microcurvature parts, by which the focuses of the incident light on the respective microcurved parts are dispersed. The diffusion angle is thereby increased and the hot spotting is decreased.
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