PURPOSE: To inexpensively constitute a compact telephoto lens large in diameter and high in performance by arranging an achromatic concave lens system constituted of a single group consisting of two lenses on the back of a semiaprochromatic convex lens system constituted of a single group consisting of a convex lens and a concave lens so as to separate both the lens systems by a prescribed distance.

CONSTITUTION: The titled lens system is provided with the semiapochromatic convex lens system constituted of a single group consisting of two convex and concave lenses and the achromatic concave lens system constituted of a single group consisting of two concave and conves lenses and arranged on the back of the semiapochromatic convex lens system so as to be separated by the prescribed distance and satisfied with a condition shown by the equation I. Provided with the focal distances of respective lens systems are f1 and f2, the rates of residual secondary chromatic aberration are K1, K2 and a mutual distance is D. Since the achromatic convex lens system is extremely inexpensive as compared to the semiapochromatic convex lens system and the residual secondary chromatic aberration of the concave lens system is surely corrected by the concave lens system and the focal distances are extended, the compact telephoto lens having a large diameter and high performance can be inexpensively produced.