| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens system where the number of lenses and optical performance is well-balanced and which is compact and obtains excellent optical performance though it has a zoom ratio (variable power ratio) being about 3 by adopting negative-leading type two groups which are negative and positive in order from an object side. SOLUTION: In the zoom lens system, a first lens group comprises two lenses, that is, a negative lens 11 and a positive lens 12 in order from the object side, and a second lens group comprises three lenses, that is, a positive lens 21, a negative lens 22, and a positive lens 23 in order from the object side, and at least the object-side positive lens 21 and the negative lens 22 are cemented together. The zoom lens system satisfies following conditional expressions (1) and (2). (1) 1.5<f<SB>2G</SB>/(f<SB>T</SB>/f<SB>W</SB>)<3.0, (2) 1<f<SB>2G</SB>(m<SB>W</SB>-m<SB>T</SB>)/(f<SB>T</SB>/f<SB>W</SB>)<3, provided that f<SB>2G</SB>; the focal length of the second lens group, f<SB>W</SB>; the focal length of an entire system at a short focal length extremity, f<SB>T</SB>; the focal length of the entire system at a long focal length extremity, m<SB>W</SB>; the lateral magnification of the second lens group at the short focal length extremity, and m<SB>T</SB>; the lateral magnification of the second lens group at the long focal length extremity. COPYRIGHT: (C)2006,JPO&NCIPI
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