Zoom lens

In a zoom lens consisting of a first positive lens group, a second negative lens group, a third positive lens group and a fourth positive lens group arranged in this order as viewed from the object field side, wherein the first lens group functions as a focusing unit, the second lens group functions as a variator for changing the magnification by moving along the optical axis in a linear fashion, the third lens group functions as a compensator for maintaining at a predetermined position the image plane which is variable with the movement of said second lens group, and the fourth lens group functions as a relay lens, and wherein said first lens group is composed of a front component constitututed by a positive lens and a rear component constituted by a positive lens and a negative lens cemented together with the resulting power being positive and the cemented surface being concave toward the object side, the improvement being characterized in that said zoom lens satisfies the following conditions:

• ##EQU4## wherein, f1, f2, f3 and f4 are the focal lengths of said first, second, third and fourth lens groups, respectively;
• fW is the shortest focal length of the total system offered by zooming;
• fT is the longest focal length thereof;
• f1F is the focal length of the front component of said first lens group;
• f1R is the focal length of the rear component thereof;
• r1 and r2 are radii of curvature of the first and second surfaces of said front component, respectively, r4 is the radius of curvature of the cemented surface of said rear component of the first lens group, and r3 and r5 are radii of curvature of the surfaces at the object side and at the image side of said rear component, respectively;
• and n2 is the refractive index of the positive lens constituting said rear component of the first lens group and n3 is the refractive index of the negative lens constituting said rear component of the first lens group.