IMAGE FORMING OPTICAL SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide an image forming optical system in which even though a diagonal angle of view is about 130°or more, distortion aberration is as small as 15% or less, F number is as bright as 2.8, and the number of sheets of lenses is small. SOLUTION: The image forming optical system comprises, 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 having the negative refracting power, and a second lens 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 directed toward the image side that is concave at least in the vicinity of the optical axis; and further, the following conditions (1) and (2) are satisfied: 1.0<¾fG1¾/FA<10 (1) and 1.0