ABSOLUTE CALIBRATION OF OPTICAL FLATS THROGOUT THE SELF COMPARISON AND IMAGE PROCESSING |
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| Jose Sánchez, Ruiz Gerardo, Sergio Padilla, Benjamin Valera |
- Abstract:
- Optical flats are required for spreading accuracy to mechanical and optical instruments, ordinarily by optical interference. Traceability of optical flats is ordinarily made by Fizeau interferometer. Traceability of this one requires higher accuracy flats, not available in secondary laboratories. These laboratories can accede to absolute self-calibration principles, by a method proposed by Bernard, who compares three flats among them through Zernike polynomials, representing these last their topographies.
Two problems are found when the process is intended to set up: (a) the Zernike polynomials have not easy geometric meaning and direct equivalence with CAD entities; (b) neither fringes nor levels of gray of interferograms have direct equivalences with the shape of flats or virtual membranes.
For modelling shapes we adopted the self calibration concept of Bernard, but using b-splines models with ring shape, instead Zernike. This substitution offer important algebraic simplifications and possibilities for exporting shapes to CAD; supporting validation.
For converting interferograms to shapes of membranes, three major problems are present: the aspect of patterns, the ambiguity in inflection areas, and the adequate interpretation of gray scales.
After applying low pass filters to brightness, two methods were applied: (a) heuristic genetic, (b) inverse sine correlation of gray for relief. Success in interpretation of shape have been by now better than 75%. - Keywords:
- self-calibration, optical flats, interpherograms conversion
- Download:
- IMEKO-WC-2009-TC8-030.pdf
- DOI:
- -
- Event details
- Event name:
- XIX IMEKO World Congress
- Title:
Fundamental and Applied Metrology
- Place:
- Lisbon, PORTUGAL
- Time:
- 06 September 2009 - 11 September 2009