| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens system which has a zoom ratio of 4 times or more and an about 30°half field angle at a short-focal-length end and is constituted of a small number of lens elements and whose front lens has a small diameter. SOLUTION: This zoom lens system comprises a 1st positive lens group, a 2nd negative lens group, a 3rd positive lens group, and a 4th positive lens group. For zooming from the wide-angle end to the telephoto end, all the lens groups move so that the gap between the 1st and 2nd lens groups, the gap between the 2nd and 3rd lens groups, and the gap between the 3rd and 4th lens groups increase and the gap between the 1st and 3rd lens groups does not vary, and the 4th lens group takes a U-turn track along which the 4th lens group moves toward the object side after temporarily moving toward the image plane side and satisfies a conditional inequality (1) 0.02<Δ×4/fw<0.2. In the conditional inequality (1), fw is the focal length of the whole system at the wide-angle end andΔ×4/fw is the movement quantity of the 4th lens group (considered to be positive when the 4th lens group moves toward the image plane side based upon the lens position at the wide-angle end) when the focal length varies from fw to 1.5×fw. COPYRIGHT: (C)2004,JPO
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