Patent ID: 8842378

Claim:
An imaging lens comprising: a first lens having positive refractive power; a second lens having negative refractive power; a third lens having negative 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 curvature radius of a surface thereof on the object side is positive and a curvature radius of a surface thereof on the image plane side is negative, said third lens is formed in 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 negative, said fourth lens is formed in a shape so that the 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, a whole lens system has a focal length f, and said first lens has the surface on the object side away from the surface of the fourth lens on the image plane side by a distance L 14 on an optical axis so that the following expression is satisfied: 0.5 <L 14 /f≦ 0.708, and said second lens is formed in 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 are both negative.