Patent ID: 7158310

Claim:
An objective lens system for microscope comprising: a first lens unit comprising at least a cemented lens component; and a second lens unit comprising at least a cemented lens component, wherein the cemented lens component in said first lens unit consists of a positive lens element and a negative lens element having a concave surface on the image side, wherein the cemented lens component in the second lens unit consists of a negative lens element having a concave surface on the object side and a positive lens element, and wherein said objective lens system satisfies the following conditions (1), (2), (3), (4) and (5): v d ( L 1 p )− v d ( L 1 n )>20 (1) v d ( L 2 p )>75 (2) −0.007 <{θCt ( L 2 p )−{θ Ct ( L 2 n )}/{ v d ( L 2 p )− v d ( L 2 n )}<0 (3) 15<f<55 (4) | f ( L 2)/ f |<4 (5) wherein the reference symbol v d (L 1 p ) represents an Abbe's number for the d-line of the positive lens element of the cemented lens component in said first lens unit, the reference symbol v d (L 1 n ) designates an Abbe's number for the d-line of the negative lens element having the concave surface on the image side of the cemented lens component in said first lens unit, the reference symbol V d (L 2 p ) denotes an Abbe's number for the d-line of the positive lens element of the cemented lens component in said second lens unit, the reference symbol V d (L 2 n ) represents an Abbe's number for the d-line of the negative lens element having the concave surface on the object side of the cemented lens component in said second lens unit, the reference symbol θCt(L 2 p ) designates a partial dispersion ratio for the t-line of the positive lens element of the cemented lens component in said second lens unit, the reference symbol θCt(L 2 n ) denotes a partial dispersion ratio for the t-line of the negative lens element having the concave surface on the object side of the cemented lens component in said second lens unit, the reference symbol f(L 2 ) represents a focal length of the cemented lens component in said second lens unit and the reference symbol f designates a focal length of the objective lens system as a whole: the partial dispersion ratio θCt being given by the following equation: θ Ct =( nC−nt )/( nF−nC ).