GRIS (GREGOR Infrared Spectrograph), the grating spectrograph is installed in the 1.5-meter GREGOR telescope located at the Observatorio del Teide in Tenerife. The spectrograph has a standard Czerny-Turner configuration with parabolic collimator and camera mirrors that belong to the same conic surface. Although nothing prevents its use at visible wavelengths, the spectrograph is mostly used in combination with the infrared detector of the Tenerife Infrared Polarimeter (TIP-II) in standard spectroscopic mode as well as for spectropolarimetric measurements. A slit scanner allows to scan some 60 arcsec. The slit length also corresponds to some 60 arcsec, with a sampling of 0.13 arcsec.
It operates in the range 1.0–2.3 μm. The experience at the German Vacuum Tower Telescope (VTT), located at the same observatory, demonstrated that the most used spectral regions are those at 1.083μm (including the photospheric Si I and the chromospheric triplet He I) and at 1.565μm (with a number of iron lines including a line with g=3). As an example for the 1.565μm region: Five accumulations of 30ms exposure time each in the 4 polarimetric states yields a signal-to-noise ratio of 1000. In this case one scan step takes 3 sec.