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Interferometric Test Data Notes
The interferometric test data results and phase maps for Galaxy Optics primary mirrors are the product of multiple interferogram fringe averaging. Phase Shift Fringe Analysis software is employed for the analysis of fringe data obtained from several individual interferograms. Data sets are averaged to determine the PV wavefront, RMS wavefront, Strehl ratio and to generate the 3-D wavefront phase map. Fringe averaging removes the errors introduced by air currents. This technique is used by all major manufactures of large observatory class telescope optics. The interferogram shown on each test data page is a sample from the data set of 6 or more.
The primary optics manufactured at Galaxy Optics are tested in the horizontal optical axis using an optical mounting sling. The sling contacts the optic on the lower 180-degree circumference.
Horizontal axis testing of large thin optics induces stress flexure errors, commonly called "Potato Chip". The most common stress flexure error is astigmatism. The personnel at Galaxy Optics thoroughly test every optic to determine if the optical surface has true astigmatism. Astigmatism that is not induced by mounting stress is always removed during optical figuring. John Hudek has studied astigmatism and stress induced astigmatic flexure for many years and is proficient in detecting true astigmatism and removing it from optical surfaces. A portion of the test stand astigmatism is sometimes subtracted from the fringe analysis. The subtraction of any optical aberration from the data reduction is always noted on the test data page.
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