Patent ID: 8817387

Claim:
An imaging lens comprising: a first lens having negative refractive power; a second lens having positive 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 curvature radius of a surface thereof on the image plane side is positive, 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 side are both negative, said third 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 first lens has a focal length f1 so that the following conditional expression is satisfied: −3.0< f 1/ f<− 1.5 where f is a focal length of a whole lens system, said second lens has the surface thereof on the object side away from the surface thereof on the image plane side by a distance d3 that is defined as a distance on an optical axis from the surface of the second lens thereof on the object side to the surface of the second lens on the image plane side so that the following conditional expression is satisfied: 1.0≦ d 3/ f< 2.0, and said third lens has a focal length f3 and the fourth lens has a focal length f4 so that the following conditional expression is satisfied: | f 3/ f 4|<0.8.