| 摘要 |
PURPOSE:To reduce and eliminate effects caused by breaks, etc., in measurement of a surface shape of a non-spherical lens or the like, by making a focal length of an objective lens variable according to existence of breaks relative to miscounts of an interferometer measurements based on breaks and foreign substances on the specimen. CONSTITUTION:A focus variable lens 11 is inserted between an 1/4-wavelength plate 4 and a convex lens 5 in an optical diameter of a surface shape gauge, and a signal from a fringe meter 7 is fed into a signal processor 12. Its output is introduced into a voltage supply unit 13 and a voltage corresponding to a signal is made available to be applied to the variable focus lens 11. In order to avoid this situation, the areas shown by the dotted lines are specified and a signal is issued when a locus of signal is emerged into this area. A signal is introduced into a voltage supplying unit 13 and a voltage is provided in such a way that the focus variable lens 11 becomes a convex lens and thus the focal length of the convex lens 5 is elongated substantially.
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