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30 September 1994 Comparison of metrology methods for large astronomical secondary mirrors
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Abstract
The secondary mirrors required for 8-meter class telescopes have increased apertures and must fit with faster primary mirrors. As dome seeing has been improved, the wavefront accuracy requirements have become significantly tighter than for previous instruments. These requirements as a set yield a different list of criteria for the determination of the final test configuration. In addition,k the desire to reduce the weight of the secondary, to either increase the first mechanical resonance mode of the spider or to decrease the inertia for chopping, has led to the use of structured mirror substrates. The importance of mechanical analysis of the support of both the secondary and the test optics becomes crucial. As part of an existing contract, a trade study was undertaken to evaluate various methods for testing convex hyperboloids of 1.4-meter aperture. Included in this discussion is a unique, compressed Hindle test. This test uses two auxiliary lenses to allow the use of a sub-sized Hindle sphere for full aperture testing. This test was demonstrated on the WIYN telescope secondary mirror fabrication. The final result of a trade study will vary from institution to institution due to differences in existing test equipment, funding methods, and overall goals. However, the starting point will be similar.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
W. Scott Smith and George W. Jones "Comparison of metrology methods for large astronomical secondary mirrors", Proc. SPIE 2263, Current Developments in Optical Design and Optical Engineering IV, (30 September 1994); https://doi.org/10.1117/12.188007
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