Patent ID: 8630047

Claim:
An imaging lens, comprising: a first lens having positive refractive power; a second lens having negative refractive power; and a third lens having positive refractive power arranged in the order from an object side to an image plane side, wherein said first lens has a shape so that a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are both positive, said second lens has a shape so that a curvature radius of a surface thereof on the object side is negative and a curvature radius of a surface thereof on the image plane side is positive, said third lens has a shape so that a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are both positive, said first lens has a focal length f 1 , said second lens has a focal length f 2 , said third lens has a focal length f 3 , said first lens and said second lens have a composite focal length f 12 , and said second lens and said third lens have a composite focal length f 23 so that the following conditional expressions are satisfied: f 1 <|f 2| f 1 <f 3 −1.0 <f 12 /f 23<−0.1.