Objective lens system for microscope

Claim 1

An objective lens system for a microscope comprising, sequentially from an object side: a first lens group having positive refracting power; a second lens group shiftable in an optical-axis direction; and a third lens group, wherein said first lens group has a cemented lens component comprising a plano-convex lens element with its plane surface toward the object side and a meniscus lens element with its concave surface toward the object side, said second lens group has a first sub-group having positive refracting power and a second sub-group having negative refracting power, said second sub-group has a negative meniscus lens element with its concave surface toward an image side, said third lens group has a meniscus cemented lens component with its concave surface toward the image side, and said objective lens system satisfies the following conditions: ##EQU3## where f: the focal length of the whole system, f 2 : the focal length of said second lens group, β: the lateral magnification of said microscope objective lens, n 1 : the refractive index of said plano-convex lens element of said first lens group, n 2 : the refractive index of said meniscus lens element of said first lens group, R 1 : the radius of curvature of an object-side lens surface of said meniscus lens element of said first lens group, R 2 : the radius of curvature of an image-side lens surface of said negative meniscus lens element of said second sub-group, R 3 : the radius of curvature of an image-side lens surface of said cemented lens component of said third lens group, d 1 : the air spacing between said first and second lens groups, and d 2 : the air spacing between said second and third lens groups.