15 July 2016 A collimated beam projector for precise telescope calibration
Author Affiliations +
The precise determination of the instrumental response function versus wavelength is a central ingredient in contemporary photometric calibration strategies. This typically entails propagating narrowband illumination through the system pupil, and comparing the detected photon rate across the focal plane to the amount of incident light as measured by a calibrated photodiode. However, stray light effects and reflections/ghosting (especially on the edges of filter passbands) in the optical train constitute a major source of systematic uncertainty when using a at-field screen as the illumination source. A collimated beam projector that projects a mask onto the focal plane of the instrument can distinguish focusing light paths from stray and scattered light, allowing for a precise determination of instrumental throughput. This paper describes the conceptual design of such a system, outlines its merits, and presents results from a prototype system used with the Dark Energy Camera wide field imager on the 4-meter Blanco telescope. A calibration scheme that blends results from at-field images with collimated beam projector data to obtain the equivalent of an illumination correction at high spectral and angular resolution is also presented. In addition to providing a precise system throughput calibration, by monitoring the evolution of the intensity and behaviour of the ghosts in the optical system, the collimated beam projector can be used to track the evolution of the filter transmission properties and various anti-reflective coatings in the optical system.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Michael Coughlin, Michael Coughlin, T. M. C. Abbott, T. M. C. Abbott, Kairn Brannon, Kairn Brannon, Chuck Claver, Chuck Claver, Peter Doherty, Peter Doherty, Merlin Fisher-Levine, Merlin Fisher-Levine, Patrick Ingraham, Patrick Ingraham, Robert Lupton, Robert Lupton, Nicholas Mondrik, Nicholas Mondrik, Christopher Stubbs, Christopher Stubbs, "A collimated beam projector for precise telescope calibration", Proc. SPIE 9910, Observatory Operations: Strategies, Processes, and Systems VI, 99100V (15 July 2016); doi: 10.1117/12.2231677; https://doi.org/10.1117/12.2231677


SWIR at the Nordic Optical Telescope: NOTCam
Proceedings of SPIE (August 15 2000)
APO 3.5-meter remote observing program--2002 and beyond
Proceedings of SPIE (January 01 2002)
SOFIA observatory performance and characterization
Proceedings of SPIE (September 26 2012)
Data reduction pipelines for the Very Large Telescope
Proceedings of SPIE (June 28 2006)

Back to Top