Improved telescope focus using only two focus images

Gregory Barrick; Tom Vermeulen; James Thomas

doi:10.1117/12.787649

23 July 2008 Improved telescope focus using only two focus images

Gregory Barrick, Tom Vermeulen, James Thomas

Proceedings Volume 7018, Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation; 70183V (2008) https://doi.org/10.1117/12.787649
Event: SPIE Astronomical Telescopes + Instrumentation, 2008, Marseille, France

Abstract

In an effort to reduce the amount of time spent focusing the telescope and to improve the quality of the focus, a new procedure has been investigated and implemented at the Canada-France-Hawaii Telescope (CFHT). The new procedure is based on a paper by Tokovinin and Heathcote and requires only two out-of-focus images to determine the best focus for the telescope. Using only two images provides a great time savings over the five or more images required for a standard through-focus sequence. In addition, it has been found that this method is significantly less sensitive to seeing variations than the traditional through-focus procedure, so the quality of the resulting focus is better. Finally, the new procedure relies on a second moment calculation and so is computationally easier and more robust than methods using a FWHM calculation. The new method has been implemented for WIRCam for the past 18 months, for MegaPrime for the past year, and has recently been implemented for ESPaDOnS.

Citation Download Citation

Gregory Barrick, Tom Vermeulen, and James Thomas "Improved telescope focus using only two focus images", Proc. SPIE 7018, Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 70183V (23 July 2008); https://doi.org/10.1117/12.787649

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