| 摘要 |
PURPOSE:To decrease the uneven colors over the entire part of a screen so that the uniformity of colors can be assured by constituting the screen of Fresnel lenses which change focal lengths in an inclination direction according to the degree of diagonal incidence of video light. CONSTITUTION:The color uniformity is obtd. only at the point of the focal length conforming to the projection distance of a screen to be diagonally entered with the video light even if an ordinary circular Fresnel lens is used. The position in the perpendicular direction of the Fresnel screen 1 is divided to, for example, 10 parts A-J in this embodiment and the focal lengths of the Fresnel lenses in the respective parts A-J are set at the projection distances aA-aJ in the case of rectangular projections. The screen is constituted by joining such Fresnel lenses A-J to one piece. The difference in white balance, i.e., uneven colors according to the places on a diagonal incident video projector screen are thereby considerably decreased and the color uniformity is assured.
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