Telescope calibration facility (TCF)

The Telescope Calibration Facility (TCF) was designed to support the NIST Stars project by providing a facility to radiometricly calibrate long focal length instruments. The TCF consists of a source room, a 40-meter tunnel, and a 40-meter viewing hall. The source room contains a variety of laser and broadband light sources which can be fiber coupled into an integrating sphere. An irradiance meter calibrated at the SIRCUS facility or the Spectral comparator facilities (SCFs) is used to measure the irradiance from the sphere. A telescope with a detector (CCD camera or spectrometer) at the focal plane is placed on a sled in the viewing hall and observes the light from the source room. An encoder on the sled allows precise changes in the source-telescope distance. Knowledge of the irradiance from the source and the source-telescope distance allow the irradiance calibration to be transferred to the telescope-detector system.