Positioner using optical relay for the MOSAIC Instrument

MOSAIC is a versatile multi-object spectrograph that will use the widest possible field-of-view provided by the ELT (Extremely Large Telescope). It will have three operating modes that cover observations in visible and infrared light for more than a hundred sources simultaneously by three hundred positioners on the focal plane. The larger size of the patrol area does not allow the use of optical fibers and the light of the pointed galaxies is send to the fiber bundles through the hollow arms of the positioner. An optical relay composed of several mirrors and lenses is integrated inside the arms and routes the light to the fiber bundles located in the base of each positioner. This solution has the advantage that a local ADC (Atmospheric Dispersion Corrector) can be directly integrated in the base of the positioner in front of the fiber bundles. Composed of two rotating prisms, the dispersion of the different wavelengths is corrected and the whole light spectra is re-focalized in the fiber bundles.