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Measurement of lens characteristics

Image Number 4 for United States Patent #5469261.

Method and apparatus for measuring the following lens characteristics: (a) curvature of the front and back surfaces of the lens; (b) physical thickness; and (c) index of refraction of the lens to determine the front vertex power, back vertex power; and the lens material. In particular, an embodiment of one aspect of the present invention for measuring the index of refraction of the glass includes: (a) a source of a substantially spatially coherent beam of radiation and having a short temporal coherence length; (b) a beamsplitter to provide a sample beam and a reference beam in response to the beam; (c) a translatable retroreflector which reflects the reference beam; (d) a holder to hold the material in the path of the sample beam, the holder including a retroreflector which reflects the sample beam back through the material and a caliper apparatus to measure the thickness of the material where the sample beam passes through; (e) a detector which detects the reflected reference beam and the reflected sample beam to produce a detector output signal; and (f) an analyzer which determines a position of the translatable retroreflector in response to the detector output signal and which determines the index of refraction of the material in response to the position of the translatable reflector means and the thickness of the material.

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