| 摘要 |
A lens-barrel optical system of the present invention is a lens-barrel optical system for guiding a beam emerging from an objective optical system in a focused state to an eyepiece optical system, which includes (i) a deflecting prism having three internal reflecting surfaces arranged in a triangular prism, the deflecting prism successively reflecting a beam incident in a first direction parallel to the optical axis of the objective optical system by the three reflecting surfaces to let the beam travel in a substantially M-shaped optical path, thereby letting the beam emerge in a second direction opposite to the first direction; and (ii) a reflector for reflecting the beam emerging from the deflecting prism to guide the beam to the eyepiece optical system. The inventor found out the way of naturally setting the eyepiece optical system at a low level without using an imaging lens and with decreasing the number of reflections in order to avoid flare and deterioration of optical image and also in order to avoid an increase of the size of the apparatus itself. Therefore, the observer's eye level can be set at a freely low position.
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