Patent ID: 8482862
Filing Date: 2013-07-09
Classification: G02B

Abstract:
1. A variable power optical system for a stereomicroscope comprising, in order from an object: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having negative refractive power, the second lens group including, in order from the object, a front group having negative refractive power and a rear group having an achromatic cemented lens including a positive lens and a negative lens, the second lens group and the third lens group moving in opposite directions along an optical axis at least in a part of a variable power block, and the following conditional expressions being satisfied: where f2 denotes a focal length of the second lens group, f2F denotes a focal length of the front group, q2 denotes a form factor of a negative lens disposed closest to the object in the front group, the form factor q2 is defined by q2=(r22+r21)/(r22−r21), where r21 denotes a radius of curvature of an object side lens surface of the negative lens in the front group, and r22 denotes a radius of curvature of an image side lens surface of the negative lens in the front group.