| 摘要 |
A variable-focus lens system that is small in size and permits attainment of high zooming ratio while maintaining high performance. In order from the object side, there are therein a first, positive lens group; a second, negative lens group; a third, positive lens group; a fourth, positive lens group; and a fifth, negative lens group; all of the lens groups move toward the object side in such fashion as to cause the distance between the first and second lens groups to increase, the distance between the second and third lens groups to decrease, the distance between the third and fourth lens groups to increase, and the distance between the fourth and the fifth lens groups to decrease, when the positional state of the lens changes from the extreme wide-angle state to the extreme telephoto state. At this time, the second lens group and the fourth lens group move in integral fashion during a change in the positional state of the lens, an aperture stop is arranged between the second and third lens groups, and the aforesaid third lens group moves during short-distance focusing. Suitable ranges for the widths of the second through fourth lens groups are defined by means of conditional expressions.
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