| 摘要 |
The invention relates to a zoom lens which, albeit being of simplified construction, makes sure brightness and holds back fluctuations of astigmatism, and facilitates making sure being fast and the angle of view and the zoom ratio at the wide-angle end. The zoom lens comprises a first group G1 of positive power, a second group G2 of negative power and a third group G3 of positive power, with a stop S between the second group G2 and the third group G3. Upon zooming from the wide-angle end to the telephoto end, the first group G1, the second group G2, and the third group G3 moves; the second group G2 moves toward the object side after moving toward the image side; the first group G1 and the third group G3 are positioned on the object side at the telephoto end with respect to the wide-angle end. The first group G1 comprises one negative lens and one or two positive lenses, and the second group G2 comprises a first negative meniscus lens convex on its object side, a second negative lens wherein the image side surface is larger in the absolute value of a curvature than the object side surface, and a third positive lens wherein the object side surface is larger in the absolute value of a curvature than the image side surface. Upon focusing from a far distance to a near distance, the second group G2 moves.
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