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Spectroradiometric Calibration of Telescopes using Laser Illumination of Flat Field Screens



Steven W. Brown, Claire E. Cramer, Keith R. Lykke, Allan W. Smith, John T. Woodward IV, Peter Doherty, Emilio Falco, Christopher W. Stubbs


It is standard practice at many telescopes to take a series of flat field images prior to an observation run. Typically the flat field consists of a screen mounted inside the telescope dome that is uniformly illuminated with a broadband light source. These flat field images are useful for characterizing the relative response of CCD pixels to light passing through the telescope optics and filters, but carry limited spectral information and are not calibrated for absolute flux. We present the results of performing in situ, spectroradiometric calibrations of a 1.2 m telescope at the Fred Lawrence Whipple Observatory, Mt. Hopkins, AZ. To perform a spectroradiometric calibration, a laser, tunable through the visible to near infrared, was coupled into an optical fiber and used to illuminate the flat field screen in situ at the telescope facility. A NIST traceable, calibrated photodiode was mounted on the telescope to measure the spectral flux reaching the aperture. For a particular filter, images of the screen were then captured for each laser wavelength as the wavelength was tuned over the filter bandpass. Knowledge of the incident flux then allows the relative responsivity of each CCD pixel at each wavelength to be calculated.
Proceedings Title
Ground-based and Airborne Telescopes III
Conference Dates
June 27-July 2, 2010
Conference Location
San Diego, CA, US
Conference Title
SPIE -Astronomical Instrumentation Proceedings


astrophysics, calibration, laser, Telescope


Brown, S. , Cramer, C. , Lykke, K. , Smith, A. , Woodward IV, J. , Doherty, P. , Falco, E. and Stubbs, C. (2010), Spectroradiometric Calibration of Telescopes using Laser Illumination of Flat Field Screens, Ground-based and Airborne Telescopes III, San Diego, CA, US (Accessed July 23, 2024)


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Created July 14, 2010, Updated October 12, 2021