| 摘要 |
PROBLEM TO BE SOLVED: To facilitate fine adjustment of a focusing position by keeping the moving amount per unit time of the focal point of a telescopic optical system moved by the movement of a focusing lens at almost fixed speed regardless of the position of the lens on an optical axis. SOLUTION: A motor-driven focus switch 40 disposed on the body of an arithmetic level 10 is connected to an arithmetic operation and control circuit 23. The switch 40 constitutes an auxiliary motor-driven focus mechanism finely adjusting to the focusing position after focusing on a collimation object by AF operation. According to the manipulated variable and the operation direction of an operation lever manually operated, an AF motor 31 is driven to move the focusing lens 12 along an optical axis. When the switch 40 is turned on, the moving amount per unit time of the focal point of the telescopic optical system moved by the movement of the lens 12 is kept at almost fixed speed regardless of the position of the lens 12 on the optical axis, so that the fine adjustment of the focusing position is easily performed in such control.
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