Immersion microscope objective

Claim 1

A microscope objective having an object side, comprising, in order from the object side: a first lens unit of positive refractive power including a cemented lens comprising a plano-convex lens and a meniscus lens including a concave surface directed toward the object side; a second lens unit including a cemented lens comprising three lens elements a negative lens element, a positive lens element, and a negative lens element; a third lens unit including a cemented lens; a fourth lens unit including a cemented meniscus lens comprising a concave surface directed toward an image side of said microscope objective; and a fifth lens unit including a cemented meniscus lens comprising a negative lens and a positive lens and comprising a concave surface directed toward the object side; wherein said microscope objective satisfies the following conditions: n.sub.2 -n.sub.1 >0.1 (1) n.sub.13 -n.sub.12 >0.15 (2) f/f.sub.1 >0.65 (3) |f/f.sub.4 |<0.2 (4) -0.8<F.sub.B /D<-0.3 (5) wherein n 1 and n 2 are the respective refractive indices of the plano-convex lens and the meniscus lens having a concave surface directed toward the object side in said first lens unit; wherein n 12 and n 13 are the respective refractive indices of the negative and positive lenses in said fifth lens unit; wherein f 1 , f 4 and f are the respective focal lengths of said first lens unit, said fourth lens unit and the microscope objective; wherein F B is back focus of the microscope objective; and wherein D is distance from a first lens surface of the microscope objective to a final lens surface of the microscope objective.