An improved collimation algorithm for the Large Binocular Telescope using source extractor and an on-the-fly reconstructor

Douglas L. Miller; Andrew Rakich; Torsten Leibold

doi:10.1117/12.930472

17 September 2012 An improved collimation algorithm for the Large Binocular Telescope using source extractor and an on-the-fly reconstructor

Douglas L. Miller, Andrew Rakich, Torsten Leibold

Author Affiliations +

Proceedings Volume 8444, Ground-based and Airborne Telescopes IV; 844459 (2012) https://doi.org/10.1117/12.930472
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

A recent upgrade of the LBTO’s Wavefront Reconstruction algorithm in the Active Optics system has proven to reduce the collimation time by a substantial amount and to provide a much more stable telescope collimation as observing conditions change. The new reconstruction algorithm uses Source Extractor to detect the spots in a Shack-Hartmann wavefront sensor camera image. With information about which Shack spots are detected, a reconstructor matrix is calculated on-the-fly that only includes the illuminated sub-apertures. This drastically improves the wavefront reconstruction for a highly aberrated wavefront when many sub-apertures contain no information. This is generally the situation at the beginning of the night when the collimation of the telescope is set only from models rather than on-sky information and occasionally when a new observational target is acquired. Similarly, the undersized tertiary mirror can cause vignetting of the pupil seen by the Shack-Hartmann wavefront sensor for far off-axis guide stars and again some sub-apertures have no wavefront information. We will present a brief description of the Active Optics system used at the Gregorian focal stations at the LBTO, discuss the original wavefront reconstruction algorithm, describe the new Source Extractor algorithm and compare the performance of these two approaches in several conditions (low signal to noise, highly aberrated wavefront, vignetted pupil, poor seeing).

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Douglas L. Miller, Andrew Rakich, and Torsten Leibold "An improved collimation algorithm for the Large Binocular Telescope using source extractor and an on-the-fly reconstructor", Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 844459 (17 September 2012); https://doi.org/10.1117/12.930472

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KEYWORDS

Reconstruction algorithms

Wavefronts

Wavefront sensors

Collimation

Telescopes

Image sensors

Cameras

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