The MTR2 is made of a predispersor (“SP1” first one on the left part), forming a lowres spectrum on the wavelength selector (so called the “mask plate”). From there, only the selected bandwiths travel to the highres echelle spectrograph (right part), ending over the MTR cameras at the SP2 output (one bandwith per camera).
The optical layout along Y is fixed (no changes, never). The ruling of the gratings are along Y only and the dispersion of both spectra is along Z only. The entrance slit is fixed (but for its width), and such are the collimators and camera mirrors.
The moving parts are:
In short:
Data and formulae for the MTR2 can be found in the following document:
THEMIS spectrograph (auth: CLM)
These tools allow the observer to quick check the feasibility of a setup