| 摘要 |
PROBLEM TO BE SOLVED: To obtain a lens device for projection where unnecessary light is little radiated even in the case of setting a short focus and which has excellent resolution by specifying lens constitution for preventing the reflection on the outer periphery part of a concave lens. SOLUTION: A face-to-face distance D between the lens surfaces S11 on a screen 14 side of a lens element 6, disposed nearest to a video generating source out of plural lens elements, and the video display surface P1 of a video generating source is allowed to satisfy n.D>=0.48fO with respect to the focal distance fO of the entire system of the projection lens device assuming that the average refractive index of a medium space 7 between the lens surface S11 and the video display surface P1 is (n). Then, the absolute value|RD|of the radius of curvature RD of the lens surface S11 is allowed to satisfy 0.61 fO<=|RD|<=0.44fO.n with respect to the focal distance fO of the entire system of the projection lens device. Thus, a phenomenon that a light beam emitted from the concave lens once is reflected on the outer periphery part of the concave lens and becomes a stray light is restrained without impairing the resolution characteristic of the projection lens device itself or peripheral light quantity.
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