1. A reflective beam splitting objective for a microscope optical system, comprising: an optical axis for the system; a primary mirror on the optical axis, said primary mirror having a generally concave reflective surface including first and second portions; a secondary mirror on the optical axis, said secondary mirror having a generally convex reflective surface positioned so as to reflect an energy beam to or from the reflective surface of said primary mirror, said secondary mirror reflective surface including first and second portions; an intercepting mirror having a reflective surface positioned off the optical axis at a skew thereto so as to redirect energy to or from said first portion of said secondary mirror; said primary mirror, said secondary mirror and said intercepting mirror positioned to form first, second and third image planes for first, second and third images, respectively, said first image plane being located a finite distance off the optical axis at a skew thereto, said second image plane located on the optical axis a finite distance from the reflective surface of said primary mirror, said third image plane located on the optical axis a finite distance from the reflective surface of said secondary mirror; said intercepting mirror having minimum practical physical separation from the secondary mirror so as to intercept as little as possible radiant energy passing between the second image plane, the second portion of the primary mirror, the second portion of the secondary mirror and the third image plane; and said intercepting mirror being positioned sufficiently away from the secondary mirror along the optical axis so as not to block radiant energy forming said first and second images that passes between the first image plane, the first portions of said primary and second mirrors and the second image plane.