| 摘要 |
PROBLEM TO BE SOLVED: To provide a projection optical system capable of obtaining a satisfactory projected image of a size in the range of about 60 to 100 inches through short-distance projection. SOLUTION: The projection optical system PO projects a display image of a display element DS on a screen SC with enlargement and varies a distance of projection on the screen SC to display the images at a varying projection magnification. The projection optical system PO includes a refractive optical system LG composed of refractive lenses and having a positive optical power and a concave-surfaced mirror MR disposed to the screen SC side of the refractive optical system LG, forms an intermediate image in the space between the refractive optical system LG and the concave-surfaced mirror MR, includes at least one optical element movable for focusing, has a plane-symmetric reflective surface as the reflective surface of the concave-surfaced mirror MR, and fulfills conditional formula 4°<θ1<20°(whereθ1 represents the angle of incidence, as measured on the cross-section of the concave-surfaced mirror MR along the plane of symmetry thereof, at which the ray, among the rays incident on the screen SC when projection is performed at the shortest distance, that forms the smallest angle with a line normal to the screen surface is incident on the concave-surfaced mirror). COPYRIGHT: (C)2008,JPO&INPIT
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