| 摘要 |
PROBLEM TO BE SOLVED: To obtain a low-cost telephoto zoom lens system for single lens reflex camera, which has about 4 zoom ratio and has a relatively short overall length of lenses. SOLUTION: The lens system comprises three positive, negative, and positive lens groups arranged in order from the object side. At the time of zooming from short focal length side to long focal length end, all the lens groups are moved so as to have long focus sides placed nearest to the object side, and the space between the first and second lens groups is increased, and the space between the second and third lens groups is reduced. The third lens group comprises a positive 3a-th lens group on the object side and a negative 3b-th lens group on the image surface side with the longest air space part in the short focal length end as the reference, and the 3a-th lens group has at least one aspherical surface. The zoom lens satisfies conditional formulas 1.7<fw/f3<2.5 and -0.5<fw/f3b<-0.2 where fw is the focal length of the entire system in the short focal length end and f3 is the focal length of the third lens group in the short focal length end and f3b is the focal length of the 3b-th lens group in the short focal length end. COPYRIGHT: (C)2004,JPO
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