PURPOSE:To achieve the improvement of operating characteristic and the prevention of the degradation of spherical aberrations by constituting the rear lens group with stationary and movable lens groups and providing a stop mechanism to the operating member for adjusting its distance. CONSTITUTION:A rear lens group L2 is constituted by a stationary lens group L21 and a movable lens group L22. The lens group L22 is held to a moving barrel 4 slidably fitted to the inner side of a guide barrel 3. An operating member 5 for adjusting its distance is fitted turnably to the outside of the guide barrel 3 and has a cam groove 5a. When the member 5 is turned at the adjusting the distance, the moving barrel 4 is pushed by the cam groove 5a with its roller 7 being held engaged in the guide groove 3a and comes to slide linearly in the optical axis direction, thus changing the position of the lens group L22 held to the moving barrel 4 on the optical axis and changing the imaging position of the entire lens system on the optical axis.
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