Patent ID: 7532416

Claim:
An imaging lens system for forming an optical image of an object on a light receiving surface of a solid-state image sensor, comprising, in order from an object side: an aperture diaphragm; and three lens elements which are a first lens element having a positive optical power and a convex surface on an image side, a second lens element having a negative optical power and being a meniscus lens whose object side has a concave shape, and a third lens element having a positive optical power and being a meniscus lens whose object side has a convex shape, wherein the following conditional expressions are satisfied: 1.5 <|fd/f 2 d |<2.3 (1) 0.5 <|fd/f 3 d |<1.1 (2) −2.2<( r 21 +r 22 )/( r 21 −r 22 )<−1.3 (3) −2.1<( r 31 +r 32 )/( r 31 −r 32 )<−1.7 (4) wherein, fd is a composite focal length of an entire imaging lens system to d-line in mm, f 2 d is a focal length of the second lens element to the d-line in mm, f 3 d is a focal length of the third lens element to the d-line in mm, r 21 is a radius of curvature of an object side surface of the second lens element in mm, r 22 is a radius of curvature of an image side surface of the second lens element in mm, r 31 is a radius of curvature of an object side surface of the third lens element in mm, and r 32 is a radius of curvature of an image side surface of the third lens element in mm, and wherein the following conditional expressions are satisfied: 1.4 <|fd/f 1 d |<2.0 (7) 0.3<( r 11 +r 12 )/( r 11 −r 12 )<0.7 (8) wherein, f 1 d is a focal length of the first lens element to the d-line in mm, r 11 is a radius of curvature of the object side surface of the first lens element in mm, and r 12 is a radius of curvature of an image side surface of the first lens element in mm.