| 摘要 |
PURPOSE:To prevent a drop in performance accompanying variable power, by using a symmetrical lens system, in which plural lens groups are symmetrically arranged about a diaphragm, as a lens system and respectively displacing two lens group from each other at the time of variable power movement. CONSTITUTION:A symmetrical lens system is used as a projecting lens 6 and the lens system is constituted of a front lens frame 11 holding the lenses G1 and G2 of the 1st group, intermediate lens frame 12 holding the lenses G3 and G4 of the 2nd and 3rd lens groups, rear lens frame 13 holding the lenses of G5 and G6 of the 4th group, and rotation-free operating ring 14. The front lens frame 11 and the rear lens frame 13 are coupled with each other by means of a screw section 15 and the intermediate lens frame 12 is inserted into the rear lens frame 13 under a rotation-free and movement- free condition. The operating ring 14 is put on the recessed sections at the outer peripheral surfaces of the frames 11 and 13 under a rotation-free condition. When a lens base 18 is moved along a guide shaft 19, the 2nd pin 17 is moved in the direction normal to the optical axis under the guidance of the cam surface 20a of a cam member 20. Accordingly, the operating ring 14 is rotated and the 2nd and 3rd lens groups G3 and G4 are moved, and then, relative positions of the lenses G3 and G4 to the 1st and 4th lens groups G1, G2, G5, and G6 can be changed automatically. |
