| 摘要 |
PROBLEM TO BE SOLVED: To obtain a simple and compact imaging optical system with low f-number. SOLUTION: The imaging optical system is provided with a block lens 5 having three reflection surfaces arranged in order of a first reflection surface 7, a second reflection surface 8 and a third reflection surface 9 in the optical path order of an incident light beam from a lens group 4 constituted of a lens having positive power. The reflection surfaces of the block lens 5 are arranged without blocking the incident light beam, and arranged so that luminous flux reflected on the first reflection surface 7 and made incident on the second reflection surface 8, and luminous flux reflected on the third reflection surface 9 may cross partially at least. COPYRIGHT: (C)2008,JPO&INPIT
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