Patent ID: 6839186

Claim:
An objective lens comprising, in order from the object side: a first lens group having positive refractive power and formed of, in order from the object side, two positive lens elements and an achromatic set of paired lens elements formed of a negative lens element and a positive lens element; a second lens group having negative refractive power; and a third lens group having positive refractive power, the surface of the third lens group nearest the object side being convex; wherein the following Conditions (1)-(4) are satisfied 0.45<|f G1 |/f<0.9 Condition (1) 0.3<|f G2 |/f<0.7 Condition (2) 0.15<|R G31 |/f<0.6 Condition (3) 0.4<D G2G3 /f<0.8 Condition (4) where f is the focal length of the objective lens, f G1 is the focal length of the first lens group, f G2 is the focal length of the second lens group, R G31 is the radius of curvature of the surface of the third lens group nearest the object side, and D G2G3 is the on-axis distance between the second lens group and the third lens group.