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.
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Figure: The INT Intermediate Dispersion Spectrograph