| 摘要 |
A zoom lens system for use as a copying lens, for example, comprises first to sixth elements arranged in this order from front to rear with a stop disposed between the third and fourth elements. The first element is a positive lens convex to the front and the second element is a negative lens concave to the front. The first and second elements together form a first stationary lens group having negative power. The third element is a positive lens and forms a first movable lens. The sixth, fifth and fourth elements are reverse duplicates of the first, second and third elements. The fourth element forms a second movable lens, and the fifth and sixth elements together form a second stationary lens group. The lens system is axially movable as a unit between fixed image and object planes. The first and second movable lenses are axially movable in response to the axial movement of the entire lens system to vary the magnification of the image. The following three conditions are satisfied. 0.4<fV/f1.0<0.61 (1) -0.55<fV/r5=fV/-r9<0.3 (2) 0.72<d9/d4<0.39 (3) wherein fV represents the focal length of the movable lenses, f1.0 represents the focal length of the entire lens system when it is adjusted for unit magnification, r5 and r9 respectively represent the radii of curvature of the surfaces of the movable lenses facing the stationary lens groups, d4 represents the axial space between the first stationary lens group and the first movable lens, and d9 represents the axial space between the second stationary lens group and the second movable lens.
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