Patent ID: 7589905

Claim:
An optical system comprising: a first negative lens element disposed nearest a front side; and a first positive lens element whose front surface resides within a distance 0.4 L from a surface nearest the front side toward a rear side of the optical system having a total lens length L, wherein the first negative lens element is composed of a material satisfying the following conditions: Ndn1>1.65 θ gFn 1−(0.6438−0.001682 ×νdn 1)>0.001 where Ndn1, νdn1, and θgFn1 denote a refractive index for the d-line, an Abbe number for the d-line, and a partial dispersion ratio for the g- and F-lines, respectively, of the material of the first negative lens element, and wherein the first positive lens element is composed of a material satisfying the following conditions: Ndp<1.78 νdp<50 θ gFp− (0.6438−0.001682 ×νdp )<0 where Ndp, νdp, and θgFp denote a refractive index for the d-line, an Abbe number for the d-line, and a partial dispersion ratio for the g- and F-lines, respectively, of the material of the first positive lens element.