Electro-optical scanning system

A defocusable electro-optical system for scanning the quasi-specular surface of an object to be examined with a light beam to produce a reflection light pattern that depends on the relative reflectivity of the different components which make up the surface, said system comprising:

• A. a light source producing an illumination beam;
• B. an objective for focusing light on said object surface;
• C. a scanning mechanism to direct said illumination beam through said objective to focus said beam onto said surface when said surface lies in the focal plane which is perpendicular to the optical axis of the objective, said object being subject to axial displacement relative to said plane;
• D. a photodetector;
• E. means to direct the beam reflected from said surface through a field stop onto said photodetector which yields a signal depending on the relative reflectivity of said components as the illustrated beam scans across said surface, said field stop limiting the size of the viewed area when the object surface lies in the focal plane;
• and
• F. means illuminating the viewed object surface in a manner imaging thereon an image of the light source comparable in size to the field stop whereby, when the object surface lies in the focal plane, the light source image is coincident therewith, and when the object surface is axially displaced from the focal plane and is out of focus, the light source image assumes an aerial position between the objective and the object surface and is relayed by the objective to function as a virtual stop, said virtual stop serving to delete that portion of the rays reflected from the object surface which otherwise would cause the image of the object to blur, thereby to limit defocus-blurring of the object image.