Optical Logic Inc.

Kantatsu Co., Ltd.

Sumio Fukuda

Hitoshi Hirano

Yoji Kubota

Kenichi Kubota

Yoshio Ise

Ichiro Kurihara

An imaging lens includes a first lens Lthat has a biconvex shape near an optical axis and has positive refractive power, a second lens Lthat has a biconcave shape near the optical axis and has negative refractive power, a third lens Lthat has a shape of a meniscus lens directing a concave surface thereof to an object side near an optical axis and has positive refractive power, and a fourth lens Lthat has a biconcave shape near the optical axis and has negative refractive power, arranged in this order from the object side. When the whole lens system has a focal length f and the fourth lens Lhas a focal length f, the imaging lens of the invention satisfies the following expression:&#x2212;0.7&#x3c;4/&#x3c;&#x2212;0.1.

Imaging lens

An imaging lens includes a first lens having negative refractive power; a second lens having negative refractive power; a third lens; a fourth lens; and a fifth lens. The first lens has a positive curvature radius on an image plane side. The second lens has a sharp convex surface, and a positive curvature radius on the image plane side. The third lens has a positive curvature radius on the object side and a negative curvature radius on the image plane side. The fourth lens has a negative curvature radius on the object side and a positive curvature radius on the image plane side. The fifth lens has a positive curvature radius on the object side and a negative curvature radius on the image plane side, and an aspheric surface.

An imaging lens includes an aperture stop ST, a first lens Lthat is shaped to form a meniscus lens that directs a convex surface to the object side near an optical axis and has positive refractive power, a second lens Lthat is shaped to form a meniscus lens that directs a convex surface to the object side near the optical axis and has negative refractive power, a third lens Lthat is shaped to form a meniscus lens that directs a concave surface to the object side near the optical axis and has positive refractive power, and a fourth lens Lthat is shaped to form a meniscus lens that directs a convex surface to the object side near the optical axis, arranged in this order from an object side to an image side. When the first lens Lhas a focal length f1 and the second lens Lhas a focal length f2, the imaging lens is configured such that a relationship 0.3&#x3c;|f1/f2|&#x3c;0.7 is satisfied.

An imaging lens, although compact, has satisfactorily corrected aberrations. The imaging lens is configured by disposing, in sequence from the object side, a stop (ST); a first lens (L), which has a double convex shape near the optical axis; a meniscus-shaped negative second lens (L) which has near the optical axis a convex surface facing the object side; a meniscus-shaped positive third lens (L) which has near the optical axis a concave surface facing the object side; and a positive fourth lens (L) which has a double convex shape near the optical axis. In the configuration, the refractive power of the first lens (L) is greater than the refractive power of each of the second lens (L), the third lens (L), and the fourth lens (L).

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Tochigi, Japan

Sumio Fukuda