IMACS: The Inamori-Magellan Areal Camera and Spectrograph on Magellan-Baade

The Inamori-Magellan Areal Camera and Spectrograph (IMACS) is a wide-field, multipurpose imaging spectrograph on the Magellan-Baade telescope at Las Campanas Observatory. IMACS has two channels f/2 and f/4, each with an 8K x 8K pixel mosaic of CCD detectors, that service the widest range of capabilities of any major spectrograph. These include wide-field imaging at two scales, 0.20 '' pixel(-1) and 0.1 '' pixel(-1), single-object and multislit spectroscopy, integral-field spectroscopy with two 5 '' x 7 '' areas sampled at 0.20 '' pixel(-1) (Durham IFU), a multiobject echelle (MOE) capable of N similar to 10 simultaneous full-wavelength R approximate to 20,000 spectra, the Maryland-Magellan Tunable Filter (MMTF), and an image-slicing refomiatter for dense-pack multislit work (GISMO). Spectral resolutions of 8 < R < 5000 are available through a combination of prisms, grisms, and gratings, and most modes are instantly available in any given IMACS configuration. IMACS has a spectroscopic efficiency over 50% in f/2 multislit mode (instrument only) and, by the A Omega figure of merit (telescope primary surface area times instrument field of view), IMACS scores 5.7 m(2) deg(2), compared with 3.1 for VIMOS on VLT3 and with 2.0 for DEIMOS on Keck2. IMACS is the most versatile, and for wide-field optical spectroscopy the most powerful spectrograph on the planet.