| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens system for a compact digital camera whose zoom ratio is≥4 and whose half field angle at the end of a short focal distance is≥30°. SOLUTION: The zoom lens system is constituted of four groups being positive, negative, positive and positive in order from an object side. In the case of zooming from the end of the short focal distance to the end of a long focal distance, all the movable lens groups (including a state where four groups are fixed) are moved from an image side to the object side so that space between a 1st lens group and a 2nd lens group is increased, space between the 2nd lens group and a 3rd lens group is decreased, and space between the 3rd lens group and a 4th lens group is increased. The zoom lens system satisfies following conditional expressions (1) and (2); (1) 0.5<|f2|/f3<1.0 (f2<0) and (2) 2<m3t/m3w<4. Provided that fi means the focal distance of an i-th lens group (i=1 to 3), m3t means the paraxial lateral magnification of the 3rd lens group at the end of the long focal distance and m3w means the paraxial lateral magnification of the 3rd lens group at the end of the short focal distance. COPYRIGHT: (C)2004,JPO
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