17 July 2008 Use of field aberrations in the alignment of the Large Binocular Telescope optics
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Abstract
It is now well-known that measurement of field-aberration, and in particular the asymmetric field-astigmatism, is required to break the degeneracy of tip-induced and de-centre-induced aberration that exists when only on-axis misalignment aberrations are considered. This paper discusses the application of the measurement of field-aberrations to the alignment of LBT optics. This application ranges from the use of wide field out-of-focus images to determine corrector tip for the red and blue prime-focus correctors, to the use of data acquired by off-axis Shack-Hartman wavefront sensors to actively reposition the hexapod-mounted primary and secondary mirrors so as to simultaneously remove both de-centre and tip/tilt such that the only remaining field-astigmatism has rotational symmetry about the centre of the detector. Also introduced is a novel method to calculate the misalignment aberrations based on an extension of the plate-diagram analysis. It is shown that this method is readily applicable to the calculation of misalignment aberrations for systems of three-or-more powered mirrors, with almost no more computational difficulty than that of the two-mirror case. Results are discussed, as well as work in progress in this area.
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A. Rakich, A. Rakich, J. M. Hill, J. M. Hill, C. J. Biddick, C. J. Biddick, D. L Miller, D. L Miller, T. Leibold, T. Leibold, "Use of field aberrations in the alignment of the Large Binocular Telescope optics", Proc. SPIE 7012, Ground-based and Airborne Telescopes II, 70121L (17 July 2008); doi: 10.1117/12.789902; https://doi.org/10.1117/12.789902
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