| 摘要 |
The invention has for its object to use a zoom system that comprises a reduced number of lens elements, is compact and simplified, and has high image-formation capability, thereby achieving thorough size reductions in video cameras or digital cameras. A zoom lens for use on an electronic imaging system comprises a negative first lens group G 1 , an aperture stop S, a positive second lens group G 2 and a positive third lens group G 3 . Upon zooming from the wide-angle end to the telephoto end of the zoom lens, the second lens group G 2 moves only toward the object side of the zoom lens and the third lens group G 3 moves in a locus different from that of the second lens group G 2 . The second lens group G 2 is made up of a positive first lens element having an aspheric surface on its object side, a negative second lens element, a positive third lens element and a negative fourth lens element. The first and second lens elements are cemented together, and the third lens group G 3 moves independently for focusing. The second lens group G 2 satisfies condition (1) with respect to the Abbe numbers of the third and fourth lens elements, condition (2) with respect to the shape of the third lens element, and condition (3) with respect to the composite focal length of the third and fourth lens elements.
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