Patent ID: 8363338

Claim:
A fixed focal length optical lens system, comprising a lens group and a diaphragm, wherein: said diaphragm is located in front of said lens group, said lens group comprising three lenses, respectively the first, the second and the third lens, which are sequentially arranged as a “negative-positive-positive” separated focal power system, said first lens is a plano-concave negative lens, said second lens is a positive meniscus lens, and said third lens is a double convex positive lens, wherein a concave surface of said second lens faces towards said diaphragm and a convex surface of said second lens faces away from said diaphragm, and a fixed focal length of the entire optical system is f, focal lengths of the first, the second and the third lens are respectively f 1 , f 2 , and f 3 , and the ratio between the focal length of each lens and the focal length f of the entire optical system satisfies the following requirement: −0.6 <f 1 /f<− 0.4; 1.0 <f 2 /f< 1.2; 0.6 <f 3 /f< 0.8.