Zoom lens having closeup focusing control

Claim 1

A zoom lens comprising: a focusing lens part consisting of a front movable lens group, an intermediate movable lens group and a fixed lens group arranged in this order from the front; a zooming part being positioned on the image side of said focusing lens part and consisting of a variation lens group and a compensation lens group; and an image forming lens being positioned on the image side of said zooming part; whereby, letting f 1 denote the focal length of the front movable lens group, and f 2 the focal length of the intermediate movable lens group, and with the positions which the front and intermediate movable lens groups occupy when focused to infinity regarded as reference positions, letting a denote the distance from the principal point of the front movable lens group located in the reference position to an object, and d the interval between the secondary principal point of the front movable lens group in the reference position and the primary principal point of the intermediate movable lens group in the reference position; as the two movable lens groups are moved to effect focusing for an object, letting S denote the amount of movement of the front movable lens group from the reference position and t the amount of movement of the intermediate movable lens group from the reference position, the movement amount S and the movement amount t satisfy the following relation: ##EQU5## wherein X = CFφ 2 - Cφ 1 φ 2 S y = - afφ 2 + aφ 1 φ 2 s + cf - cφ 1 s - cg + c 2 s - cfφ 2 s + cφ 1 φ 2 s 2 z = ag + afφ 2 s - aφ 1 φ 2 s 2 - ec - cfs + cφ 1 s 2 a = 1 - φ 1 d B = -d C = -φ 1 φ 2 d + φ 1 + φ 2 D = 1 - dφ 2 E = a · A + B f = aφ 1 + 1 G = aC + D φ 1 = 1/f 1 , φ 2 = 1/f 2 .