An optical arrangement was designed for use in a system being developed for automated inspection of superfinished spherical surfaces. Light from a helium neon laser is passed through a spatial filter to remove unwanted intensity variations in the beam profile, and the light proceeding from the filter is collimated by a lens of appropriate focal length. A second lens is used to converge the collimated light to a virtual focal point at the center of the sphere to be inspected. The geometry is such that all the rays incident on the highly reflective spherical surface are reflected back along their paths, and the retroreflected light is diverted by a beamsplitter. A third lens is used to focus the diverted light to a point on the face of a photodetector array capable of measuring light intensity as a function of radial and angular coordinates.
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