Patent ID: 8848299

Claim:
An optical module having an object side and an image side; the module comprising, from the object side to the image side: a positive meniscus lens having a focal length F 1 and comprising first and second optical surfaces, the first optical surface being convex and facing the object side, and the second optical surface being concave and facing the image side; a plano-convex lens having a focal length F 2 and comprising third and fourth optical surfaces, the third optical surface being flat and facing the object side, and the fourth optical surface being convex and facing the image side; the four optical surfaces having their curvatures defined by the equation: Zi =CURV i Yi 2 /(1+(1−(1+ Ki )CURV i 2 Yi 2 )½)+( Ai ) Yi 2 +( Bi ) Yi 4 +( Ci ) Yi 6 +( Di ) Yi 8 where: i is the surface number (i=1 to 4); for the i-th surface, Zi is the distance between a point on the aspheric surface at the height of Yi above the optical axis and a plane tangent to the aspheric surface at the intersection of this surface with the optical axis; Ki is a constant called the conic constant of the i-th surface; CURVi is the curvature if the i-th surface at the intersection of this surface with the optical axis; where CURV3=0; Ai, Bi, Ci, Di, are, respectively, the aspheric coefficients of the 2 nd , 4 th , 6 th , and 8 th order of the i-th surface, with A3=0, B3=0, C3=0, D3=0; Ri is the effective radius of aperture of the i-th surface; the two lenses being such that 0.35 <F 1 /F 2<0.90 0.30<Conv2/Conv<0.70 0.50 <M 1 /M 2<1.20 where Mi=(1−(1+Ki)(CURVi) 2 (Ri) 2 )½ Conv2 is the convergence of the second lens and Conv is the convergence of the complete lens module.