Patent ID: 8023204

Claim:
A compact short back focus imaging lens system with two lenses, along an optical axis from an object side to an image side, comprising: an aperture stop; a first lens with positive refractive power that is a meniscus lens with two aspherical surfaces and a convex surface facing the object side; a second lens with negative refractive power that is a meniscus lens with two aspherical surfaces and a convex surface facing the image side; an IR cut-off filter; and an image sensor; wherein the following conditions are satisfied: 0.25 ≤ d 2 + d 4 + d 6 f s ≤ 0.4 - 0.3 ≤ f 1 f 2 ≤ - 0.01 0.25 ≤ bf TL ≤ 0.4 wherein d 2 is distance on optical axis from the image side of the first lens to the object side of the second lens, d 4 is distance on optical axis from the image side of the second lens to the object side of the IR cut-off filter, d 6 is distance on optical axis from the image side of the IR cut-off filter to the image plane of the image sensor, f s is effective focal length of the imaging lens system, f 1 is focal length of the first lens, f 2 is focal length of the second lens, bf is back focal length of the imaging lens system, and TL is distance from the aperture stop to an image plane.