PURPOSE: To compensate various aberrations by allowing an optical system consists of the 1st positive meniscus lens having a convex surface on an object side, the 2nd biconcave negative lens, and the 3rd biconvex positive lens successively from the object side to meet specific requirements.

CONSTITUTION: This triplet lens consists of the 1st, the 2nd, and the 3rd lenses L1, L2, and L3 successively from the object side and meets various requirements shown by inequalities I WXII. In the inequalities, Σd is the overall length of the lens, (f) is the composite focal length of the lens, and (ri) is the radius of curvature of the (i)th surface from the object side; and (di) is the (i)th gap, (ni) is the refractive index of the (i)th lens from the object side, and νi is the Abbe number of the (i)th lens from the object side. Further, (fi) is the focal length of the (i)th lens from the object side.