| 摘要 |
A fast zoom lens system includes a positive first lens group, a negative second lens group, a positive third lens group and a positive fourth lens group, in this order from the object. Upon zooming from the short focal length extremity to the long focal length extremity, a distance between the positive first lens group and the negative second lens group increases, a distance between the negative second lens group and the positive third lens group decreases, and a distance between the positive third lens group and the positive fourth lens group decreases. The fast zoom lens system satisfies the following conditions; <?in-line-formulae description="In-line Formulae" end="lead"?>6.0<F1/fw<10.0 (1)<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>3.0<F3/fw<8.0 (2)<?in-line-formulae description="In-line Formulae" end="tail"?> wherein f 1 designates the focal length of the positive first lens group; f 3 designates the focal length of the positive third lens group; and fw designates the focal length of the entire fast zoom lens system at the short focal length extremity.
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