| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system capable of reversing the direction of an image in a small installation space without using a roof face. SOLUTION: All of 1st, 2nd and 3rd reflection planes 1 to 3 are rectangular, and they are arranged with such a positional relation that they make a part of each inside face of three side faces of a triangle pyramid. A reference light beam L made incident on the 1st reflection plane 1 is successively reflected by the three reflection planes, then, the light is emitted. The optical path of the reference light beam L when the beam is made incident on the 1st reflection plane 1 exists in the same plane as that when the beam is reflected by the 3rd reflection plane 3, and the optical paths intersect each other at an angle ofγin the reference plane. The image reversing optical system is provided with a function of reversing the direction of the image in a one dimensional direction with respect to the vertical direction.
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