| 摘要 |
PURPOSE:To obtain a zoom lens which has a constitution being suitable for an auto focus although it is a rear focus system, is compact and has a high performance, by constituting said lens of three groups, and allowing it satisfy a specific condition. CONSTITUTION:The titled zoom lens is constituted so that the first group lens is a cemented lens having positive power, the second group lens has negative power, and consists of separated single lenses of negative, negative and positive, the third group consists of the front part having positive power and the rear part having negative power, the front part a positive and positive meniscus cemented lens and a positive lens, and the rear part consists of single lenses of positive and negative, and the first and the third groups and the second group move on the optical axis as one body and independently, respectively, by which the focal distance is varied, and by moving the rear part of the third group to an image side, focusing is executed. In this case, this lens is allowed to satisfy the conditions of an expression I. In such a way, a zoom lens system of a rear focus system of a constitution being compact and suitable for an auto focus is obtained.
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