In optical manufacturing, it is vital to properly correlate measurements to their corresponding location on the lens surface.
Such measurements are typically used to identify locations where excess material should be removed, and therefore any errors in knowing the location of the measurement will result in poor quality of manufactured optics.
Shack-Hartman wavefront measurements are one of the more accurate metrology tools used in optical manufacturing
Using a Shack-Hartman sensor sometimes involves a number of relay lenses that can flip the measured waveform relative to the test optics. In addition, the sensor and the test optics can be rotated with respect to each other, the test optics can be flipped, measurements can be done in reverse, or all of these situations can be combined.
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