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The flat field fiber system (also known as the “wide flat” system) is used to project broadband light onto the main spectrometer CCDs. The projected light consists of a series of bands (one per echelle diffraction order), with each band being wider in cross-dispersion than the height of the orderlet stackfive orderlets from the Science, Sky and Simultaneous Cal fibers. This allows one to flat field and calibrate the response of pixels both within the orderlets, and also between and outside of the orderlets (which are normally not illuminated).

The system consists of a broadband source, a shutter, and a filter wheel (or in this case an aperture wheel). The aperture wheel is populated with various apertures, which are used to change the f/# of the beam leaving the output fiber (as shown below). This in turn changes the width of the bands in cross-dispersion on the main spectrometer CCDs and allows one to adjust the band overlap.

Note that a shutter is included to set the wide flat image exposure times.

Within the aperture wheel there is also a blank port, which allows no light to pass. This should be in-beam whenever the wide flat system is not in use, to prevent accidental stray light from entering the main spectrometer vacuum chamber from this system.

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Relevant Devices

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