| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens capable of realizing accurate autofocusing without making a lens barrel mechanism large even in the case of using a moving cam for focusing by satisfying a specified conditional expression at a telephotographing end. SOLUTION: Focusing is performed by a negative 4th lens group in a five group constitution of positive, negative, positive, negative and positive. The rotational ratio (aF/aZ) of variable power rotational; amount from the wide angle end (F=28.8) to the telephotographing end (F=126.0) to the focusing rotational amount from the infinity focusing position to the closest focusing position (R=0.08m) is set to -0.55. Then the conditional expressions 1.00<γXR/ΓXO, 10.00<ΔXTR/ΔXWR<30.00 and -1.00<aF/aZ<-0.50 are satisfied at the telephotographing end. In the expressions,γXO andγXR represent the ratio of the fine moving amount dBf of an image-formation surface to the fine moving amount dx in the optical axis direction of a focusing lens group at the infinity focusing point and the closest focusing point, andΔXWR andΔXTR represent the moving amounts in the optical axis direction of the focusing lens group required to perform focusing from the infinity state to the closest state at the wide angle end and the telephotographing end. |
