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Proceedings Paper

Analysis of curvature sensing for VISTA
Author(s): Brett A. Patterson; Will J. Sutherland
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Paper Abstract

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.

Paper Details

Date Published: 30 January 2003
PDF: 11 pages
Proc. SPIE 4842, Specialized Optical Developments in Astronomy, (30 January 2003); doi: 10.1117/12.459467
Show Author Affiliations
Brett A. Patterson, UK Astronomy Technology Ctr./Royal Observatory Edinburgh (United Kingdom)
Will J. Sutherland, UK Astronomy Technology Ctr./Royal Observatory Edinburgh (United Kingdom)

Published in SPIE Proceedings Vol. 4842:
Specialized Optical Developments in Astronomy
Eli Atad-Ettedgui; Sandro D'Odorico, Editor(s)

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