Concept for the optics in the central structure. The light from the telescope can be blocked by the instrument closing mechanism, which instead folds in light from the Calibration Unit. The optical path then goes directly to SPIFFIER, passing only the IR/VIS dichroic that splits light off to the wavefront sensors. The path can be redirected to NIX with a movable fold mirror (whose background is kept low via a turret extension of the SPIFFIER cryostat). The AO optical path is split by another dichroic that transmits light from the LGS, and reflects the rest to the NGS wavefront sensor.