Imaging lens
A compact low-priced imaging lens which offers a field of view of about 180 degrees and high optical performance. The imaging lens for a solid-state image sensor includes, in order from an object side to an image side, a first lens with negative refractive power having a convex object-side surface and an aspheric image-side surface; a second lens with negative refractive power as a double-sided aspheric lens having a concave surface on the image side; a third lens with positive refractive power; an aperture stop; and a fourth lens with positive refractive power. The first and second lenses are made of plastic material. The imaging lens satisfies conditional expressions (1) and (2) below: −65.0< f 1/ f <−17.0 (1) 0.04< f 2/ f 1<0.14 (2) where f: focal length of the overall optical system of the imaging lens f1: focal length of the first lens f2: focal length of the second lens.
1. An imaging lens in which elements are arranged in order from an object side to an image side, comprising:
a first lens having negative refractive power, a convex surface on the object side, and an aspheric surface on the image side;
a second lens as a double-sided aspheric lens having negative refractive power and a concave surface on the image side;
a third lens having positive refractive power;
an aperture stop; and
a fourth lens having positive refractive power,
wherein the first lens and the second lens are made of plastic material; and
conditional expressions (1b), (2b), (3b), (4b), and (5b) below are satisfied:
−50.76≦ f 1/ f≦− 21.63 (1b)
0.06≦ f 2/ f 1≦0.12 (2b)
6.09≦ f 3/ f≦ 7.64 (3b)
2.03≦ f 4/ f≦ 2.41 (4b)
18.01≦ TTL/f≦ 20.34 (5b)
where
f: focal length of an overall optical system of the imaging lens
f1: focal length of the first lens
f2: focal length of the second lens
f3: focal length of the third lens
f4: focal length of the fourth lens
TTL: distance on an optical axis from the object side surface of the first lens to an image plane.
2. The imaging lens according to claim 1 ,
wherein
the third lens is a meniscus lens with at least one aspheric surface having a concave surface on the image side; and
the fourth lens is a biconvex lens with at least one aspheric surface having a convex surface on the object side and the image side.
3. The imaging lens according to claim 1 ,
wherein the third lens and the fourth lens are made of plastic material.