| 摘要 |
PROBLEM TO BE SOLVED: To restrain the tilt of a moving barrel to a fixed barrel without increasing the operational torque of a focusing ring. SOLUTION: Three straight advance grooves 41 constituting a 1st straight advance groove group are formed at intervals of 120 deg. on the inner peripheral surface of a cylinder part 27 in the moving barrel 21, while a straight advance key group consisting of three straight advance keys 45 corresponding to the grooves 41 is screwed on the outer peripheral surface of the inside fixed barrel 15. Rectangular sliding parts 47 and 49 are protrusively provided at the front and rear ends of the upper surface of the key 45. The groove 41 is set so that a specified clearance (dx) (for example, about 10μ) may be formed between the basic groove width H of the groove 41 and the key 45, and the sliding parts 47 and 49 are set so that the specified clearance (dx') (for example, about 10μ) may be formed between the upper surfaces of the sliding parts 47 and 49 and the base of the key 45.
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