| 摘要 |
PROBLEM TO BE SOLVED: To obtain a rear focus type zoom lens which has excellent performance over the entire zoom area and all object distances and has a high power variation ratio. SOLUTION: The zoom lens has four lens groups, i.e., a 1st group with positive refracting power, a 2nd group with negative refracting power, a 3rd group with positive refracting power, and a 4th group with positive refracting power, varies the power from the wide-angle end to the telephoto end by moving the 2nd group toward an image plane, and corrects image plane variation accompanying the power variation by moving the 4th group and is put in focus by moving the 4th group; and a diaphragm is provided on the object side of the 3rd group, which is composed of two lenses, i.e., a positive lens made very convex to the object side and a meniscus negative lens made very concave to the image-plane side.
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