| 摘要 |
PROBLEM TO BE SOLVED: To provide an oblique projection optical system where trapezoidal distortion is not caused in an image in focusing and which performs focusing by a simple mechanism. SOLUTION: A 1st lens group Gr1 and a 2nd lens group Gr2 which are coaxial optical systems constitute a part of an axial asymmetric optical system where they are decentered each other, and project an image so that an image surface IS may be inclined to an object surface OS. The 2nd lens group Gr2 is used as a focusing lens group GrF. By moving the 2nd lens group Gr2 in parallel in the direction of an optical axis (AX2) (shown by an arrow mF), focusing is performed so that the image surface IS may be moved in parallel in a state where it keeps a tilt angleθI to the object surface OS constant.
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