| 摘要 |
PROBLEM TO BE SOLVED: To compactly constitute an image forming optical system in an observation optical device using an optical element for rotating an image. SOLUTION: This observation optical device is provided a Pechan prism for correcting image rotation 30 compensating the rotation of an object occurring by the rotation of an elevation mirror 2 and the image forming optical system forming the object image whose rotation is corrected by the prism 30. Then, a convex lens 31 is integrally arranged at the incident surface side of the prism 30. Thus, the observation optical device which is well-balanced as a whole and whose whole length and diameter are small can be obtained.
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