| 摘要 |
PURPOSE: To instantaneously change the photographing magnification of a subject while a camera and lens are held fixed by a tripoed is held fixed by specifying the constitution of first to third lens groups. CONSTITUTION: The first lens G1 is fixed, the second lens group G2 moves along a locus projecting with respect to an image plane and the third lens group G3 moves from the image side to the object side in the case of variable magnification from the wide angle end to the telephoto end. At least one lens group among the three lens groups L11 to L13 in the first lens group G1 moves along the optical axis in the case of focusing from an infinite object to a close- range object. The zoom lens is so constituted as to satisfy conditions 0.7<|f1112.F23/(f13.F)|<1.5, 0.3<|f13/f1112|<1.1 when the combined focal length of the positive lens group L11 and the positive lens group L12 is defined as f1112; the focal length of the negative lens group L13 as f13, the combined focal length of the second lens group G2 and the third lens group G3 as F23 and the focal length of the entire part of the lens system as F.
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