Patent ID: 7019920

Claim:
An imaging optical system, including an image-formation lens arrangement comprising two lenses, in order from an object side thereof, a first meniscus lens convex on an object side thereof and a second lens having positive refracting power and a convex surface on an object side thereof, the convex surface being configured such that an absolute value of a curvature of an object side-surface of said second lens is larger than an absolute value of a curvature of an image side-surface of said second lens, wherein said image-formation lens arrangement has only two lens elements in all, and further including an aperture stop located on the object side of said image-formation lens arrangement, with satisfaction of the following conditions: −0.27 <f 2 /f 1 <0.27 (1) −0.5<( r 2 −r 3 )/( r 2 +r 3 )<0.2 (2) where: f 1 is a focal length of the first meniscus lens, f 2 is a focal length of the second lens, r 2 is an axial radius of curvature of an image side-surface of the first meniscus lens, and r 3 is an axial radius of curvature of the object side-surface of the second lens.