Patent ID: 8792186

Claim:
An imaging lens comprising: a first lens having positive refractive power; a second lens having positive 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 is formed in a shape so that a surface thereof on the object side has a positive curvature radius and a surface thereof on the image plane side has a negative curvature radius, said second lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have negative curvature radii, said third lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii, said third lens is formed in the shape so that the surface thereof on the object side and the surface thereof on the image plane side are respectively formed as aspheric surfaces having inflexion points, and said first lens has a focal length f1, said second lens has a focal length f2, said third lens has a focal length f3, said first lens has the surface on the object side having the curvature radius R 1 f , and said first lens has the surface on the image plane side having the curvature radius R 1 r so that the following conditional expressions are satisfied: f 1< f 2< f 3 1.0< f 1/ f< 1.5 −0.02< R 1 f/R 1 r< 0 where f is a focal length of a whole lens system.