Patent ID: 8243129

Claim:
An objective lens comprising, in order from an object side, a front group having negative refractive power, an aperture stop, and a rear group having positive refractive power, wherein: the front group comprises, in order from the object side, a first lens which is a negative meniscus lens with a convex surface turned to the object side and a second lens which is a negative lens with a concave surface turned to the object side; the rear group comprises, in order from the object side, a positive third lens and a fourth lens made up of a positive lens and a negative lens cemented together; and the objective lens satisfies conditional expression (1) below: −0.8 <f — F/f — R<− 0.3 (1) where f_F is a focal length of the front group, and f_R is a focal length of the rear group.