Patent ID: 8456766

Claim:
A photographing optical system comprising, in order from an object side to an image side: a first lens element with positive refractive power having a convex object-side surface and a concave image-side surface; a second lens element with negative refractive power having a concave image-side surface; a third lens element with positive refractive power having a concave object-side surface and a convex image-side surface; and a fourth lens element with negative refractive power having a concave image-side surface, both the object-side and image-side surfaces thereof being aspheric, made of plastic, and at least one inflection point is formed on at least one of the object-side and image-side surfaces of the fourth lens element; wherein the photographing optical system comprises four lens elements with refractive power; a radius of curvature of the image-side surface of the fourth lens element is R 8 , a radius of curvature of the object-side surface of the fourth lens element is R 7 , an on-axis spacing between the first lens element and the second lens element is T 12 , an on-axis spacing between the second lens element and the third lens element is T 23 , a radius of curvature of the object-side surface of the third lens element is R 5 , a radius of curvature of the image-side surface of the third lens element is R 6 , the photographing optical system also comprises an aperture stop, a distance on an optical axis between the aperture stop and an image plane is SL, a distance on the optical axis between the object-side surface of the first lens element and the image plane is TTL, a maximal distance between an on-axis site on which the object-side surface of the fourth lens element projects and an on-axis vertex of the object-side surface of the fourth lens element is SAG 41 max, a maximal distance between an on-axis site on which the image-side surface of the fourth lens element projects and an on-axis vertex of the image-side surface of the fourth lens element is SAG 42 max, and they satisfy the following relations: | R 8/ R 7|<0.15; 0.35 <T 12/ T 23<0.70; 2.0<( R 5+ R 6)/( R 5− R 6)<4.5; 0.7 <SL/TTL< 1.2; and −1.30 <SAG 41max/ SAG 42max<−0.45.