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16 August 2000 Gemini facility calibration unit
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High-quality, efficient calibration instruments is a pre- requisite for the modern observatory. Each of the Gemini telescopes will be equipped with identical facility calibration units (GCALs) designed to provide wavelength and flat-field calibrations for the suite of instruments. The broad range of instrumentation planned for the telescopes heavily constrains the design of GCAL. Short calibration exposures are required over wavelengths from 0.3micrometers to 5micrometers , field sizes up to 7 arcminutes and spectral resolution from R-5 to 50,000. The output from GCAL must mimic the f-16 beam of the telescope and provide a uniform illumination of the focal plane. The calibration units are mounted on the Gemini Instrument Support Structure, two meters from the focal pane, necessitating the use of large optical components. We will discuss the opto-mechanical design of the Gemini calibration unit, with reference to those feature which allow these stringent requirements to be met. A novel reflector/diffuser unit replaces the integration sphere more normally found in calibration systems. The efficiency of this system is an order of magnitude greater than for an integration sphere. A system of two off-axis mirrors reproduces the telescope pupil and provides the 7 foot focal plane. The results of laboratory test of the uniformity and throughput of the GCAL will be presented.
© (2000) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Suzanne K. Ramsay-Howat, John W. Harris, David C. Gostick, Ken Laidlaw, Norrie Kidd, Mel Strachan, and Ken Wilson "Gemini facility calibration unit", Proc. SPIE 4008, Optical and IR Telescope Instrumentation and Detectors, (16 August 2000);


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