Patent ID: 7426079

Claim:
An optical system comprising: a refractive optical element composed of a solid material, the Abbe number νd and the partial dispersion ratio θgF of the solid material satisfying the following conditions: −2.100×10 −3 ·νd+ 0.693 <θgF , and 0.555 <θgF< 0.9; wherein a height of a paraxial marginal ray passing through a forefront lens surface of the optical system is less than, as measured from an optical axis, a maximum height of the paraxial marginal ray passing through a lens surface positioned at the rear of an intersection point of the optical axis with a paraxial chief ray, and wherein the refractive optical element is disposed at the front of the intersection point and has a shape so that the thickness of the refractive optical element at a position of about 70% of the maximum effective ray diameter is greater than a thickness of the refractive optical element on the optical axis.