| 摘要 |
PROBLEM TO BE SOLVED: To obtain an oblique projection optical system having a large angle of view, high magnification and a sufficient oblique projection angle and capable of being made compact by shortening a lens diameter and the entire length of a lens group by making the absolute value of an angle formed by a primary image surface with a secondary image surface satisfy a specified conditional expression range. SOLUTION: The image light of the secondary image surface (image surface) 2 is obliquely enlarged and projected to the primary image surface (object surface) 1 by a projection lens group 3a. A light beam forming a larger angle to the normal direction of an enlargement side image surface out of the light beams emitted from the enlargement side image surface on the eccentric plane of the lens group 3a passes through longer distance in a lens medium nearest to a reduction side. The absolute value|θi -θ0|of the angle formed by the primary image surface 1 with the secondary image surface 2 satisfy the conditional expression range|θi -θ0|<10 deg.. Thus, the entire length of the lens group 3a is made compact.
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