PURPOSE: To obtain a lens with a simple constitution which has spherical aberration and sine condition compensated excellently by allowing the lens system which consists of four elements in three groups, i.e. a positive meniscus lens, cemented lens of a positive and a negative lens, and positive meniscus lens arranged successively from a body side to meet specific requirements.

CONSTITUTION: The lens system of a three-group, four-element constitution consists of the positive meniscus lens, cemented lens of the positive and negative lenses, and positive meniscus lens successively arranged from the body side and meets the specific requirements, i.e. 3f<f1<6f, -6f<r4/(n3-n2)<-3.3f, and 13f<r7<3.3f. In this case, (f) and (f1) are the focal lengths of the whole system and the 1st group, r4 is the radius of curvature of the composition surface of the 2nd group, and n2 is the refractive index of the body-side lens of the 2nd group; and n3 is the refractive index of the image-side lens of the 2nd group, and r7 is the radius of curvature of the image-side surface of the 3rd group. Consequently, the lens of the simple constitution having spherical aberration and sine condition compensated excellently is obtained.