Patent ID: 7697220

Claim:
An image forming optical system comprising, in order from an object side, a front lens group having negative refracting power, and a rear lens group having positive refracting power, wherein the front group comprises, in order from the object side, a first lens element having the negative refracting power, and a second lens element of a meniscus form having a convex surface directed toward an image side; wherein the first lens element has an aspherical surface that is a concave surface directed toward the object side in the vicinity of the optical axis, and negative refracting power at a position on the aspherical surface becomes weak as a distance between the position and the optical axis becomes large; and a surface that is a concave surface directed toward the image side at least in the vicinity of the optical axis; and further the following conditions (1) and (2) are satisfied: 1.0 <|f G1 |/F A <10 (1) 1.0 <|f G2 /F A <10 (2) where F A is a focal length of the whole optical system, f G1 is a focal length of the front group, and f G2 is a focal length of the rear group.