Objective lens system

DETAILED DESCRIPTION A primary object of the present invention is to provide an objective lens system consisting of a single lens component and having aberrations corrected favorably within a broad range covering the offaxial region.
The objective lens system according to the present invention consists of a cemented doublet consisting, in the order from the object side, of a lens element having a concave surface on the object side and a lens element having a convex surface on the image side, comprises aspherical surfaces arranged as the first and second surfaces respectively, and is so designed as to satisfy the following condition (1): -0.
2>r.
sub.
3 /f>-0.
8 (1) wherein the reference symbol r.
sub.
3 represents radius of curvature on the image side surface of said convex lens element (the third surface) and the reference symbol f designates focal length of the objective lens system as a whole.
Further, the objective lens system according to the present invention consists of a cemented doublet consisting, in the order from the object side, of a meniscus lens element having a convex surface on the object side and a lens element having a convex surface on the object side, uses aspherical surfaces designed as at least one of the first and second surfaces, and the third surface, and is so designed as to satisfy the following condition (2): r.
sub.
3 f<-2 or 0<r.
sub.
3 /f (2) In the objective lens system according to the present invention, the locations of the aspherical surfaces and the orientations (convex or concave on the object side) of the aspherical surfaces are closely related to the radius of curvature on the third surface (radius of curvature in the vicinity of the optical axis when the third surface is designed as an aspherical surface).
When the first surface concave on the object side and the second surface convex on the object side are designed as the aspherical surfaces in the objective lens system according to the present invention, it is necessary to select a radius of curvature satisfying the condition (1) for the third lens surface so that it has relatively strong positive refractive power