PURPOSE: To correct the positive deviation of the image plane and the negative deviation of spherical aberrations at the close-up by setting a variable air spacing in a front group and reducing the variable air space along with the extending of the front group at the time of focusing as well as by satisfying predetrmined conditions.

CONSTITUTION: The focal length of the entire system in which the axial space (l) between the front group I and rear group II of the lens has changed is changed and the air space (d) changes according to the extent of extension of the front group I; moreover, these are so constituted as to satisfy conditions (1) and (2). The conditions (1) specify the ratio of the focal length of the lens system I1 positioned nearer to the object side than the variable space and the focal length of the entire system on the wide angle side and obtain a suitable divergence of on-axis luminous flux at the air space (d). Further, conditions (2) specify the on-axis space of variable space (d) and correct the degradation in the image plane. With such constitution, the positive deviation of the image plane and the negative deviation of spherical aberrations at the close up may be corrected.