Patent ID: 8194333

Claim:
An imaging lens comprising, in order from an object side to an image surface side: a first lens having positive power; a second lens composed of a meniscus lens having negative power whose lens surface facing the image surface side is concave; a third lens composed of a meniscus lens having positive power whose lens surface facing the image surface side is convex, and a fourth lens having negative power whose lens surfaces are both aspheric and lens surface facing the image surface side is concave in the vicinity of an optical axis, wherein a diffractive optical element is formed on one of the lens surfaces of the first lens or one of the lens surfaces of the second lens, wherein the first lens is a biconvex lens, and wherein when f denotes a focal length of an entire optical system, f 1 denotes a focal length of the first lens, f 2 denotes a focal length of the second lens, f 3 denotes a focal length of the third lens, φ DOE denotes power of the diffractive optical element and TL denotes a total length of the optical system, conditional expressions (1) to (5) are satisfied: 0.8< f 1/ f< 1.1 (1) −2.0< f 2/ f<− 1.8 (2) 0.8< f 3/ f< 1.2 (3) 0< f·φ DOE (4) TL/f< 1.3 (5).