The instrument laboratory is located in the fifth floor of the GREGOR building, directly below the telescope platform. All post-focus instruments are located here, with the exception of the major part of GRIS in the spectrograph room on the fouth floor. The instrument laboratory was completely reconfigured in 2020 in order to considerably improve the stability and the imaging quality of the adaptive optics relay between F3 and F4. Also, parallel obervations of several instruments in different spectral regimes has been made easier. The replacement of the former toric relay optics mirrors (M12 and M15) by off-axis paraboloid mirrors has eliminated field-dependent aberrations, mainly astigmatism and coma. Imaging between F3 and F4 is now diffraction limited for visible wavelengths throughout the field of view.
The new configuration has the following characteristics:
- More space for post-focus instruments and a future multi-conjugated AO system
- Horizontal tables for all optics with better stability and much easier adjustment
- Arrangement of the wave front sensor following M15, thereby compensating all powered optics
- 49mm diameter pupil to match existing tip-tilt and deformable mirrors
- 1:1 magnification between F3 anf F4
- Aberration-free image quality within 60 arcsec radius
- Exchangeable dichroic beam splitter in front of F4 reflects visible spectral range and transmits IR for GRIS
- No reconfiguration of GRIS entrance slit unit required
- Small angles of incidence on beamspitters for less instrumental polarization and better polarimetry
- Telecentric exit pupil
The existing pentaprisms are replaced by dichroic beam splitter plates with smaller angles of incidence. There are two plates with a transition wavelength of 650nm and 900nm, which allows observing the H-alpha spectral region either with a visible instrument or with an H-alpha channel in the slit viewing system for GRIS.
For more information see GRE-KIS-TN-0019.