The spectrograph design is based on a white pupil configuration where the main collimator and the transfer collimator are nominally both off-axis Maksutov systems, reaching a near diffraction limited optical quality along the relatively long slit required for recording four sliced spectra. At the field lens, located at the intermediate focal plane between the main- and transfer-collimators, the light is divided between a blue and red arm by a selectable dichroic.
