PURPOSE: To obtain a clear lens whose aberration is corrected excellently over a wide magnification range by permitting a lens, consisting of four lens groups, to meet prescribed requirements.

CONSTITUTION: Four lens groups are formed meeting requirements shown by inequalities (1)W(8). In those inequalities, (f) is focal length of the entire system, n1 and n6 are refractive indexes of the 1st and 4th lens groups, and ν1, ν2, ν5 and ν6 are Abbe numbers of the lens in the 1st group, the object-side lens in the 2nd group, the image-side lens in the 3rd group, and the lens in the 4th group. Further, r1, r3, r5, r6, r8 and r10 are radiuses of curvature of the object-side surface of the lens in the 1st group, the object-side and image side surfaces of the lens in the 2nd group, the object-side and image-side surfaces of the lens in the 3rd group, and the image side surfaces of the lens in the 4th group; and d3, d4, d6 and d7 are the thicknesses of both the lenses in the 2nd group and those of both the lenses in the 3rd group, and d5 is the air gap between the lenses in the 2nd and 3rd groups.