Patent ID: 8879172

Claim:
An imaging lens comprising: a first lens having positive refractive power; a second lens having negative refractive power; a third lens having positive refractive power; and a fourth lens having negative refractive power arranged in this order from an object side to an image plane side, wherein said first lens is formed in a shape so that a surface thereof on the object side is convex toward an object, said second lens is formed in a shape so that a surface thereof on the object side is concave toward the object and a surface thereof on the image plane side is convex toward the object, said third lens is formed in a shape so that both a surface thereof on the object side and a surface thereof on the image plane side are concave toward the object, said fourth lens is formed in a shape so that a surface thereof on the object side is concave toward the object and a surface thereof on the image plane side is convex toward the object, said fourth lens has a focal length f 4 and a whole lens system has a focal length f so that the imaging lens satisfies the following expression: −0.33 ≦f 4 /f<− 0.1 said third lens has a focal length f 3 so that the imaging lens satisfies the following expression: 0.15 <f 3 /f≦ 0.43 said second lens has the surface on the object side having a curvature radius R 3 and the surface on the image plane side having a curvature radius R 4 so that the imaging lens satisfies the following expression: −8.0 <R 4 /R 3<−2.0.