IMAGE-FORMING OPTICAL SYSTEM AND DISTANCE MEASURING DEVICE

摘要

A compact, adequately bright image-forming optical system is provided. The image-forming optical system has three reflecting mirrors. When the optical system is placed in an XYZ Cartesian coordinate system where the Z-axis coincides with the optical axis through the center of the visual field, the direction of the optical axis is varied in the YZ cross section while maintaining the direction of the optical axis in the XZ cross section so that the optical path incident on a second reflecting surface crosses the optical path exiting from a third reflecting surface, and the optical axis of the center of the visual field is parallel to the optical axis of the image plane. At least one of the three reflecting surfaces is an asymmetrical surface of revolution. The equivalent F number of the image-forming optical system Fno satisfies the relations 0.5<Fno(L2/L3)<1.3 where L2 is the distance between the second reflecting surface and the third reflecting surface along the optical path of the light beam along the optical axis through the center of the visual field and L3 is the distance between the third reflecting surface and the image plane along the optical path.