PURPOSE: To enable the obtaining of a bright image through both of visual diagnosis and photographing with simple construction at low cost by selectively inserting prisms havng mirrors of different reflectances in the optical path to eyepieces via objective lens.

CONSTITUTION: Prism groups 4, 4' are provided to the inside of the optical system consisting of an objective lens 1, magnifying lenses 2, 2', eyepieces 8, 8', taking lens 9, camera 10, etc. The prism groups 4, 4' comprises superposing above and below the fully transmittable prisms 4-1, 4'-1, total reflecting prisms 4-2, 4'-2, half mirror prisms 4-3, 4'-3, and fixing these to a frame 11 and are so constituted as to be made vertically movable by knobs 14, 14'. In the case of fine lines in the figure, the visual diagnosis is done through the fully transmittable prisms 4-1, 4'-1. In the case of photographing, the half mirror prism 4'-2 is moved to the specified position and the taking point is checked, after which both total reflecting prisms 4-3, 4'-3 are moved in the specified position, thence the total quantity of light of the image enters the camera 10, whereby the sharp photographing may be performed.