| 摘要 |
PROBLEM TO BE SOLVED: To provide a retro focus type wide-angle lens system which attains a long back focus compared with a focal length, an F-number of about 4, and a half viewing angle of about 45 degrees, achieves excellent optical performance from infinity to a close distance, and has superior cost performance. SOLUTION: The wide-angle lens system comprises a negative first lens group, a negative second lens group and a positive third lens group. The first lens group includes a negative meniscus lens having a convex surface facing toward the object side, and a positive lens having a convex surface facing toward the object side. The first lens group has at least one aspherical surface. The second lens group has a negative meniscus lens having the convex surface facing toward the object side, and a pair of cemented lenses having a negative lens and a positive lens which are cemented. The third lens group has a pair of cemented lenses having a negative lens and a positive lens which are cemented, and a positive lens having a convex surface facing toward the image surface side. The wide-angle lens system satisfies conditional expressions (1) 1.30<f3/f<1.70, and (2)-13.50<f2/f<-3.80, provided that f designates the focal length of the entire system, f2 designates the focal length of the second lens group, and f3 designates the focal length of the third lens group. COPYRIGHT: (C)2010,JPO&INPIT
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