Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003spie.4842..231p&link_type=abstract
Specialized Optical Developments in Astronomy. Edited by Atad-Ettedgui, Eli; D'Odorico, Sandro. Proceedings of the SPIE, Volume
Astronomy and Astrophysics
Astronomy
1
Scientific paper
VISTA is the Visible and Infrared Survey Telescope for Astronomy that has been designed by the UK ATC. The design incorporates two cameras covering the visible and near-IR wavelengths. The 4-m primary mirror has an active support system with 84 axial actuators that is used, in conjunction with the 5-axis support system for the 1.2-m secondary mirror, to maintain the image quality at seeing-limited conditions (~0.6 arcsec at Cerro Paranal, Chile). A system of curvature sensing is proposed to measure the low-order aberrations of the telescope and camera, which uses a pair of CCD arrays located at the edge of the camera focal-plane array. The analysis presented here uses simulated extra-focal images of point sources generated using the optical design program ZEMAX and demonstrates that this off-axis curvature-sensing technique will provide adequate measurements of low-order aberrations under the expected SNR, seeing conditions and field crowding. Even with the VISTA f-ratio of 3.26, an extra-focal distance of only 1 mm is shown to be sufficient to obtain rms wavefront errors accurate to a few tens of nanometres (under ideal and fully time-averaged seeing conditions). The demonstrated insensitivity to crowding means a field of 35 arcmins2, such as obtained with VISTA on a standard CCD, is sufficient to guarantee finding a suitably bright guide star.
Patterson Brett A.
Sutherland Will J.
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