| 摘要 |
PROBLEM TO BE SOLVED: To obtain an observation optical system and an image forming optical system constituted so that an observation viewing angle is wide, a focal distance is short and an intermediate image is formed one time by mutually correcting decentering aberration by two decentering prisms. SOLUTION: This system is provided with the 1st prism 10 and the 2nd prism 20. The 2nd prism 20 is provided with a 1st surface 21, a 2nd surface 22 and a 3rd surface 23. The 1st surface 21 is the incident surface and the reflection surface, the 2nd surface is the reflection surface and the 3rd surface is the emitting surface. Then, at least one out of the 1st and the 2nd surfaces is shaped to be rotation-asymmetric so that power is given to luminous flux and the aberration caused by decentering is corrected. The 1st prism 10 is provided with a reflection surface 12 an incident surface 11 and an emitting surface 13. The reflection surface 12 is shaped to be rotation-asymmetric so that the power is given to the luminous flux and the aberration caused by the decentering is corrected. Then, an intermediate image surface 4 is formed between the 1st surface of the 2nd prism and the emitting surface of the 1st prism.
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