| 摘要 |
PROBLEM TO BE SOLVED: To obtain a light, wide-angled imaging optical system by improving the imaging performance by reducing astigmatism. SOLUTION: In the imaging optical system, wherein light beams reflected by three first to third reflectors, disposed in the order of optical paths of the incident light beams form imaging planes having planes A and B that do not match each other, if a plane containing incident and reflected center main light beams of the first reflector is the plane A, a plane containing incident and reflected center main light beams of the second reflector is a plane B, and a plane containing incident and reflected center main light beams of the third reflector is the plane C, ¾n<SB>1</SB>+(1<SB>2</SB>/1<SB>2</SB>')<SP>2</SP>×n<SB>3</SB>¾/f<2 is satisfied, where n<SB>1</SB>is the astigmatism amount of the conjugate surface of the first reflector alone to an infinite-distance object plate, n<SB>3</SB>is the astigmatism amount of the conjugate surface of the third reflector alone with respect to an image plane, l<SB>2</SB>is the distance of the conjugate plane of the first reflector alone with respect to the infinite-distance object plane from the second reflector, 1<SB>2</SB>' is the distance of the conjugate plane of the third reflector alone with respect to the image plane from the second reflector, and (f) is the focal length. COPYRIGHT: (C)2009,JPO&INPIT
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