Patent ID: 6236521
Filing Date: 2001-05-22
Classification: G02B

Abstract:
An objective lens consisting of the following four lens units in sequence from the object side:a first lens unit consisting of a first lens of negative refractive power in the shape of a meniscus with a concave surface toward the image field side;a second lens unit consisting of a second lens of positive refractive power;a third lens unit consisting of a composite lens having joined together a third lens of negative refractive power with a concave surface toward the object side and a fourth lens of positive refractive power with a convex surface toward the image field side, said third lens unit having, as a whole, negative refractive power; anda fourth lens unit consisting of a fifth lens of positive refractive power,wherein on letting fi, f12, and f be the focal length of an i-th lens unit, the composite focal length of the first lens unit and a second lens unit, and the focal length of the whole objective lens system, respectively, the conditions of0.7<.vertline.f1.vertline./f<3.0,0.7<f4/f<3.0, and0.8<f12/f<2.5 are satisfied.