| 摘要 |
PURPOSE:To provide a high variable power zoom lens which is simple in construction, is compact has good aberration performance by setting the focal lengths of the 1st lens group, the 2nd lens group and the 3rd lens group respectively at specific values with respect to the focal length at a telephoto end. CONSTITUTION:The 4th lens group IV for the purpose of imaging is provided. The 2nd lens group is fixed and the 1st lens group and the 3rd lens group moved in the stage of zooming in such a way as to be nearer the object side when the zoom position is at the telephoto end than when the zoom position is at the wide angle end in the stage of zooming. The following condition equations are satisfied when the focal lengths of the 1st lens group, the 2nd lens group and the 3rd lens group are designated respectively as fI, fII, fIII and the focal length of the entire system of the telephoto end is designated as fT: 0.45<fI/fT<0.75, 0.10< ¦fII¦/fT<0.23, 0.2<fII/fT<0.35. Aberration and more particularly a spherical aberration and distortion aberration are thus corrected without increasing the number of lenses. The extent of the movement of the lens owing to zooming is decreased and the diameter of the lens is made smaller.
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