Patent ID: 8320061

Claim:
A lens system, in the order from the subject side to the image side thereof, comprising: an aperture stop; a first lens of positive refractive power having a subject-side surface and an image-side surface; a second lens of negative refractive power having a subject-side surface and an image-side surface; a third lens of positive refractive power having a subject-side surface and an image-side surface; and a fourth lens of negative refractive power having a subject-side surface and an image-side surface; the lens system satisfying the following formulae: G2R2<G2R1<0; and 0<D1/D2<9.95, where G2R1 is the curvature radius of the subject-side surface of the second lens, G2R2 is the curvature radius of the image-side surface of the second lens, D1 is the diameter of the aperture stop, and D2 is the distance from the center of the aperture stop to the center of the subject-side surface of the first lens; the lens system further satisfying the following formulae: G2R2/G3R1>1.26; G3R2/G2R1>1.05; 0.42<G2R1/F2<0.45; 1.52<G2R2/F2<1.73; G4R1>G4R2>0; and 0.53<G4R1/F<0.56, where G3R1 is the curvature radius of the subject-side surface of the third lens, G3R2 is the curvature radius of the image-side surface of the third lens, G4R1 is the curvature radius of the subject-side surface of the fourth lens, G4R2 is the curvature radius of the image-side surface of the fourth lens, F2 is the effective focal length of the second lens, and F is the effective focal length of the lens system.