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Surface Profile Error Measurement For Small Rotationally Symmetric Surfaces

The precision machine tool industry has developed processes that produce rotationally symmetric surfaces, both spheres and aspheres, with form errors on the order of 5 microinches (1/5 wave or 0.125 p.m). Precisionmachined diamondturned surfaces can have surface finishes better than 100 angstroms Ra; these surfaces may be intended to be used as an optic, or the surface may be intended to be used to meet a mechanical requirement. Regardless of their intended use, surfaces of this quality can be tested using optical test techniques such as interferometry. This paper reviews the advantages and disadvantages of the methods that have been used to measure aspheric surfaces in the Aspheric Technology department of Kodak Apparatus Division. These techniques include Fizeau and Williams interferometry, holography, stylus and optical profilometry, and null correctors.