Patent ID: 7715121

Claim:
An optical system mountable to an image pickup apparatus including an image pickup element, comprising: a negative lens disposed furthest away on an enlargement conjugation side, wherein the following condition is satisfied: 80 degrees<2ω, where 2ω (degrees) denotes an angle of view of the optical system, and wherein the following conditions are satisfied: 0.25<tan θ/tan ω<1.5, Ndn>1.65, and θ gFn −(0.6438−0.001682 ×νdn )>0.0010, where θ denotes a lens open angle of a surface of the negative lens on a reduction conjugation side, Ndn and νdn denote the index of refraction and Abbe number of a material of the negative lens for a d-line, respectively, and θgFn denotes a relative partial dispersion of the material of the negative lens for a g-line and an F-line.