| 摘要 |
PROBLEM TO BE SOLVED: To obtain a telephoto type zoom lens with a power variation ratio of about 10 while decreasing the number of lens elements and shortening the overall length by composing the zoom lens of lens groups having specified refractive index on the whole and specifying the refractive indicter of the respective lens groups and movement conditions for power variation. SOLUTION: The zoom lens consists of 1st positive and 2nd negative lens groups and a rear group which has more than one lens group and is positive on the whole. For power variation, lens groups are moved so that conditions represented as expressions are met, where D1W and D1T, and D2W and D2T are the intervals between the 1st and 2nd groups, and 2nd group and rear group at the wide-angle end and telephoto end. Further, conditions represented as expressions are met, where f2 is the focal length of the 2nd group, SKW, OTLW, andΩare the back focus, overall optical length, and half field angle at the wide-angle end, o3W and o3T the distances from the most object side lens surface to the front side principal point position of the rear group at the wide-angle end and telephoto end, fW and fT the focal lengths of the whole system, andβ2W andβ2T the image forming powers of the 2nd group.
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