Swing arm optical CMM: self calibration with dual probe shear test

Swing arm optical CMM (SOC), a profilometer with distance measuring interferometric probe for in situ measurement of the topography of aspheric has been used for measuring highly aspheric mirrors with a performance rivaling full aperture interferometric tests. Recently, we implemented a dual probe self calibration mode for the SOC. Data from the dual probes can be used to calibrate the swing-arm air bearing errors since both probes see the same bearing errors while measuring different portions of the test surface. Bearing errors are reconstructed from the shear signal with a modal estimation.