Science Operations

Instrument Characteristics


Each MODS consists of a pair of identical double–beam blue–red optimized optical spectrographs attached to the straight–through F/15 Gregorian focus of each of the LBTO 8.4 m primary mirrors. The guiding and wavefront-sensing systems are constructed as part the MODS1/2 instruments, and are located above the instrument focal planes, but within the units themselves at the instrument hatches. The calibration units are also located up near the entrance port, above the slit plane.   The optical layout of MODS1 and MODS2 are identical and is shown below.

Optical Layout

After light passes through a common slit mask (not shown) and field lens, a dichroic splits light into red and blue-optimized spectrograph channels. Each channel has its own collimator, dispersers, camera, filters, field flattener (FF) lens, and detector. The dichroic, used for dual beam spectroscopy, can be exchanged with a mirror for red-only operation or nothing for blue-only operation, extending wavelength coverage into the dichroic cross-over region (~5650Å) for one or other channel alone.