Patent ID: 6741403
Filing Date: 2004-05-25
Classification: G02B

Abstract:
A lens system comprising:three lenses juxtaposed with each other and each having refractive power, a first one of the three lenses serving with positive refractive power being a plastic lens having a front side formed with a convex surface having a radius of curvature of R1 and a rear side formed with a concave surface having a radius of curvature of R2, and |R1|a second one of the three lenses serving with negative refractive power being a plastic lens having a front side formed with a concave surface, a shape coefficient X2=((R1+R2)/(R2âˆ’R1)) being larger than 0.9; a third one of the three lenses serving with positive refractive power being a glass lens having positive refractive power; the refractive power of the first lens, the refractive power of the second lens, and a combining refractive power of the first and second lens meet the following requirements: (P1/P2)>âˆ’1.0 0>(P12/P1)>0.8 wherein P1: the refractive power of the first lens; P2: the refractive power of the second lens; P12: the combining refractive power of the first and second lens; the shape coefficient of a lens being define as Xi=(R1+R2)/(R2âˆ’R1), wherein i ranges from 1 to 3 and refers to the first to the third lenses, R1 being the radius of curvature of front surface of lens, R2 being the radius of curvature of the rear surface of lens, and R1>0 as the front surface being convex, R1<0 as the front surface being concave, R2<0 as the rear surface being convex, R2>0 as the rear surface being concave; at least one diffractive surface being formed on at least one of the plastic lens of the three lenses, and at least one aspheric surface being formed on at least one of the plastic lens of the three lenses.