| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact zoom lens system of satisfactory optical performance. SOLUTION: In the zoom lens system, a first lens group includes a diffraction element and a positive lens element. The positive lens element included in the first lens group is made of a glass material that satisfies the conditions given below: 25<(f<SB>T</SB>/H<SB>max</SB>)×N<SB>ave</SB><50 (in which N<SB>ave</SB>=Σ(N<SB>i</SB>×ϕ<SB>i</SB>)/Σϕ<SB>i</SB>), and 0.08<1G<SB>total</SB>/LDT<SB>W</SB><0.15. Here, f<SB>T</SB>represents the focal length of the entire zoom lens system in a telephoto end, H<SB>max</SB>represents the height of the maximum image, N<SB>ave</SB>represents the weighted average value of refractive indexes of positive lens elements composing the first lens group, N<SB>i</SB>represents the refractive index of the i-th positive lens element composing the first lens group,ϕ<SB>i</SB>represents the power of the i-th positive lens element composing the first lens group, LDT<SB>W</SB>represents the total thickness from the first face of the lens at a wide angle end to the final face of the lens, and the 1G<SB>total</SB>represents the total thickness from the first face of the lens to the final face of the lens composing the first lens group. COPYRIGHT: (C)2011,JPO&INPIT
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