| 摘要 |
PROBLEM TO BE SOLVED: To improve the measurement precision of a fringe scan. SOLUTION: A CCD camera 10 captures an image of interference fringes generated owing to the optical path length difference between luminous flux to be inspected and reference luminous flux. A computer while monitoring variation of a luminance signal of a certain specific pixel in the image signal outputted from the CCD camera 10 displaces a piezoactuator 18 by a fringe scan. At this time, the luminance signal of the above pixel varies. When an expected driving quantity of a Fizeau lens 43 reaches a value corresponding to 1/2 wavelength of the light emitted by the light source of the interference measuring instrument, the computer compares the luminance value before the fringe scan starts with the luminance value when the fringe scan ends. Consequently, a control error in the optical path length difference between the reference luminous flux and luminous flux to be detected is found to correct a piezocommand signal outputted at the time of a next fringe scan and a Fizeau surface 43 is precisely driven to increase the interference measurement precision.
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