Patent ID: 7460314

Claim:
A three-piece type optical lens, along an optical axis in order from an object side, comprising: a first lens element with positive refractive power that is a meniscus aspherical lens having a convex surface on an object side thereof; a second lens element with negative refractive power that is a meniscus aspherical lens having a convex surface on an image side thereof; a third lens element with negative refractive power that is a M-shaped aspherical lens having a M-shaped object side and a M-shaped image side while a central surface of the optical axis thereof is a convex surface or a concave surface; an IR cut-off filter; and an image sensor; wherein the optical lens satisfies following conditions: 0.4f≦d<0.9f 0.3 <|R 1 /R 2|<0.6 2.8≦Fno<3.6 0.2 <br/f <0.4 0.5 <f 1 /f <1 −10.0 <f 3 /f<− 2.0 wherein f is an effective focal length of the optical lens; d is distance between an object side of the first lens element and an image side of the third lens element; R 1 is a radius of curvature of the object side of the first lens element, R 2 is a radius of curvature of the image side of the first lens element, Fno is a F number of the optical lens, br is a back focal length of the whole optical lens of the present invention, f 1 is an effective focal length of the first lens element, f 3 is an effective focal length of the third lens element.