A focusing means for a zoom lens system.

摘要

When a zoom lens system is focused by moving a lens otherthan the foremost lens group, the advancing amount of the focusing lens varies according to variation in the focal length even when focusing on an object at the same object . distance. When a zoom lens system is zoomed to a certain focal length, the object distance and advancing amount of the focusing lens has a relation expressed by a function resembling the logarithmic function. The present invention enables to focus a zoom lens system using only one movement amount curve by arranging to move the focusing lens along one movement amount curve and to utilize different portions of the movement amount curve according to zooming.