The Intermediate Dispersion Spectrograph (IDS) is the principal common-user instrument at the Cassegrain focus of the INT. The IDS design is a folded-input, flat-bed instrument. It is mounted -- along with the Faint Object Spectrograph (FOS-1, see section ) -- below the Cassegrain A&G box (see section ). Figure shows the overall optical layout. Either IDS or FOS-1 operation is selected by installing or removing the folding prism, so that both spectrographs, and indeed both cameras of the IDS, albeit with different detectors, can be used consecutively during the same night. The acquisition TV camera, and autoguider, as well as the calibration and comparison lamps, above-slit neutral-density and colour filters are all located in the separate A&G unit to which the spectrograph is attached. Dekker masks, the slit assembly and below-slit filters are located within the main body of the spectrograph itself.
[ TIFF ]
Figure: The INT Intermediate Dispersion Spectrograph