| 摘要 |
A second lens group is divided into a negative second A lens group and a positive second B lens group, and the distance between the second A and B lens groups is made variable so as to correct a fluctuation in aberration caused by a change in focal length, thereby reducing the size and weight of the whole lens system, while the fluctuation in performance is kept low in the whole zoom range and whole focus range. The second lens group is constituted by the second A lens group having a negative refracting power and the second B lens group having a positive refracting power. Upon a change in focal length, the distance between the second A and B lens groups is altered so as to suppress the fluctuation in aberration mainly in a middle range. Namely, in the second lens group having the highest refracting power, a surface spacing highly sensitive to the change in aberration is altered, whereby the aberration can be corrected with a favorable balance. Specifically, as indicated by the moving loci in FIG. 1, during the movement from the wide angle end to the telephoto end, the second A and second B lens groups are moved such that the distance therebetween is narrowed in the middle range.
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