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Isaac Newton Telescope

IDS: The Intermediate Dispersion Spectrograph

First light (at ING): March 1984 (decommissioned on 17 July 2003, recommissioned on 1 August 2006).

Designed and built by: RGO

Description: The principal common-user instrument at the Cassegrain focus of the INT is the Intermediate Dispersion Spectrograph (IDS), with a choice of two cameras of different focal lengths. It is combined with the Faint Object Spectrograph (FOS), a fixed-format, efficient spectrograph designed for low resolution work.

Both the IDS and the FOS are part of the same structure: a folded-input, flat-bed instrument, with the FOS occupying the straight through position. The spectrographs hang below an Acquisition and Guidance unit. Both cameras of the IDS (and indeed the FOS) may be used during the same night. Facilities for acquisition and guidance, calibration and comparison lamps, neutral-density and colour filters are located in the A&G unit to which the spectrograph is attached. Spectrograph and A&G functions are computer-controlled, although changes of grating and collimator are manual.

The IDS has a wide selection of first-order gratings giving dispersions in the range 7-140 Å/mm. Two cameras have focal lengths of 235 and 500 mm.

In June 1988, a square-to-line reformatter (SQRIL) was tested and commissioned. Mounted in the multislit unit, it consists of an array of 100 fibres changing a 12 × 12 arcsecond grid to a line feeding an input slit to the IDS.

Time allocations:
Nights scheduled since semester 2007B

Instrument information:

Research impact:

Scientific highlights (29)

Public outreach:

Media releases (9)


Photo archive (4)

Video archive (3)

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Last modified: 08 November 2023