| 摘要 |
PROBLEM TO BE SOLVED: To constitute a zoom lens of a small number of lens elements, to reduce the lens outside diameters and to enable the zoom lens to be corrected in spherical aberration, coma aberration and astigmatism by specifying the relations between the focal length of an M-th group optical system and the combined focal length of the entire system at the wide angle end. SOLUTION: This zoom lens consists of lenses L1 to L3 and has negative refracting power. The first lens group G1 moves on the optical axis in such a manner that the moving quantity decreases gradually to the image side on the optical axis and corrects the fluctuation in the focal position at the time of zooming frome the wide angle end to the telephoto end. The second lens group G2 moves monotonously to the object side on the optical axis at the time of zooming from the wide angle end to the telephoto end. The first and second lens groups G1, G2 satisfy 1.95<|f1|<fW<2.02(f1 <0), 1.04<|f1|/f2 <1.16(f1 <0, f2 <0) when the focal length of the first lens group G1 is defined as f1 , the focal length of the second lens group G2 as f2 , the focal length of the M-th lens group (M=1, 2) as fM and the combined focal length of the entire system at the wide angle end as fW.
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