Patent ID: 8395853

Claim:
An image pick-up optical system, sequentially from an object side to an image side, comprising: a first lens element with negative refractive power, having a convex object-side surface and a concave image-side surface; a second lens element with positive refractive power; a third lens element with positive refractive power, having a convex object-side surface and a convex image-side surface; a fourth lens element with negative refractive power, having a concave object-side surface; and a fifth lens element with positive refractive power, made of plastic, and having a convex object-side surface, and at least one of the object-side surface and an image-side surface thereof being aspheric; and a stop; wherein f 2 is a focal length of the second lens element, f 5 is a focal length of the fifth lens element, R 1 is a radius of curvature of the object-side surface of the first lens element, R 2 is a radius of curvature of the image-side surface of the first lens element, D SR3 is an axial distance from the stop to the object-side surface of the second lens element, T 12 is an axial distance between the first lens element and the second lens element, and the following conditions are satisfied: 0.8< f 2 /f 5 <1.6; 1.2< R 1 /R 2 <5.0; and 0< D SR3 /T 12 <0.4.