| 摘要 |
An zooming adjustment mechanism for an optical system is provided for reducing the length of the optical system along its optical axis, and enable the size down of the optical system. A cam ring is provided for adjusting distances between a first lens and a second lens that are constituting a telescope optical system in a binocular. Each of a first cam groove and a second cam groove includes two grooves. Two first cam grooves and two second cam grooves are formed on an outer circumferential surface at a distance along the circumferential direction. The two first cam grooves and the two second cam grooves are formed on the same area of the circumferential direction about the axis of the cam ring, i.e., the axis of a main shaft direction.
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