| 摘要 |
PROBLEM TO BE SOLVED: To obtain an image formation optical system which is composed of a small-sized, high-performance prism optical system. SOLUTION: This image formation optical system has a prism member 10 which is formed of a medium whose refractive index is larger than 1 and the prism member 10 has a 1st transmission surface 14, 1st to 3rd reflection surfaces 11 to 13, and a 2nd transmission surface 15. The 2nd reflection surface 12 and 3rd reflection surface 13 are so arranged that the track of the on-axis main light beam in the prism is folded triangularly and an on-axis main light beam made incident on the 2nd reflecting surface 12 and the on-axis main light beam projected from the 3rd reflection surface 13 form crossing optical paths. At least one reflection surface among the 1st to 3rd reflection surfaces 11 to 13 has a curved surface shape giving power to luminous flux and the curved surface shape is a rotationally asymmetrical surface shape which corrects aberrations generated by eccentricity.
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