| 摘要 |
An optically compensated zoom lens particularly suited for use in a still camera. This lens system comprises positive first, negative second and positive third lens groups counting from the front of which the first and third ones are axially movable in fixedly spaced relation to each other during zooming, while the second one remains stationary together with a relay lens group that follows the third lens group, the relay lens group consisting of a negative lens with its front surface of strong divergence, and bi-convex, bi-concave and bi-convex lenses. In said first and said second lens groups, there are provided individual divergent contact surfaces configured in opposite direction of curvature to each other so as to facilitate good correction of astigmatism and distortion. For high grade imaging performance throughout the entire range of magnification, the shift of focal plane with zooming is limited within the depth of focus by fulfilling the following relationships for the three lens groups in the zoom portion: (1) 0.97 Ft<f1<1.23 Ft (2) 0.31 Ft<¦f2¦<0.42 Ft (3) 0.38 Ft<f3<0.51 Ft (4) 12<(S/M)<17 wherein f1: the focal length of the first lens group; f2: the focal length of the second lens group; f3: the focal length of the third lens group; S: the length of movement of the first and third lens groups from the wide angle setting to the telephoto setting; M: the magnification ratio; and Ft: the focal length of the entire system when in the telephoto setting.
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