| 摘要 |
PROBLEM TO BE SOLVED: To provide a zoom lens facilitating aberration correction by restraining the fluctuation of an open f-number due to variable power to be small, realizing miniaturization, higher variable power and a wider angle, and suitable for a video camera and a digital camera. SOLUTION: The zoom lens has a 1st group G1 having negative refractive power, an aperture diaphragm S whose aperture area is varied, and a 2nd group G2 having positive refractive power, varies power by changing space between the respective groups in the case of varying the power from a wide angle end to a telephoto end and has a variable power ratio≥3.4. The aperture diaphragm S moves in the same direction as the moving direction of the 2nd group G2 in the case of varying the power, and is constituted so that the maximum area of the aperture part of the aperture diaphragm S at the time of photographing may be smaller at a wide angle end than at a telephoto end. The zoom lens satisfies a conditional expression (1): -2<f<SB>1</SB>/√(f<SB>T</SB>×f<SB>W</SB>)<-1 regulating the focal distance of the 1st group G1 by the average focal distance of the zoom lens, and a conditional expression (2): 1.05<S<SB>T</SB>/S<SB>W</SB><4 regulating the ratio of the maximum area of the aperture part of the aperture diaphragm S at the time of photographing at the wide angle end and that at the time of photographing at the telephoto end. Provided that f<SB>1</SB>: the focal distance of the 1st lens group, f<SB>W</SB>: the focal distance of the entire system of the zoom lens at the wide angle end, f<SB>T</SB>: the focal distance of the entire system of the zoom lens at the telephoto end, S<SB>W</SB>: the maximum area of the aperture part of the aperture diaphragm at the time of photographing at the wide angle end and S<SB>T</SB>: the maximum value of the aperture part of the aperture diaphragm at the time of photographing at the telephoto end. COPYRIGHT: (C)2005,JPO&NCIPI
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