| 摘要 |
PURPOSE: To obtain a zoom lens of three-group constitution which is short in overall lens length and has high optical performance of a power variation ratio of 2 and an F number of nearly 4. CONSTITUTION: The zoom lens has three lens groups of a 1st group L1 with negative refracting power, a 2nd group L2 with positive refracting power, and a 3rd group L3 with negative refracting power in order from the object side and is varied in power by moving the 1st group L1 and 2nd group L2 on the optical axis, and the 2nd group L2 consists of a positive biconvex lens element 21, a negative biconcave lens element 22, and a positive lens element 23; and conditions of 0.95<β2W×β2T<1.05 and 0.25<|f22/fT|<0.5 are met, whereβ2W andβ2T are the image formation powers of the 2nd group at the wide-angle end and telephoto end, fT is the focal length of the whole system at the telephoto end, and f22 is the focal length of the lens element 22.
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