| 摘要 |
PROBLEM TO BE SOLVED: To obtain an inexpensive and high-performance zoom lens of 4 group constitution by a comparatively small number of lenses. SOLUTION: This zoom lens system is constituted of a 1st positive lens group 10, a 2nd negative lens group 20, a 3rd positive lens group 30 and a 4th positive lens group 40 in this order from the object side. Then, when zooming is executed to a long focal distance end from a short focal distance end, all of the lens groups are moved to the object side so that an interval between the groups 10 and 20 is widened, an interval between the groups 20 and 30 is narrowed and an interval between the groups 30 and 40 is narrowed. Then, the group 30 is constituted of a positive lens 3-1, a positive lens 3-2 whose strong convex surface faces the object side and a negative lens 3-3 whose strong concave surface faces the object side in turn from the object side. Besides, the conditional expression of -1.8<ϕr331<ϕw<-1.1 is satisfied. In the expression,ϕr331 represents the power of the object-side surface of the lens 3-3 of the 3rd lens group andϕw shows the power of the whose lens system at the short focal distance end.
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