Geometric model of the telescope to compute contamination on the optical surfaces. Left panel: Contamination from a point Q on the baffle wall onto a point P on M1 (bottom grey disk). Right panel: Contamination from a point Q on M2 (top grey disk) onto P. The same setup can be used to compute contamination of M1 by sublimation from the ‘front ring’ (FR), contamination of M2 from M1 and the ‘back ring’ BR, and the water flux loss through the front aperture, simply by adjusting the respective integral bounds. The blue lines indicate fixed parameters listed in Table D.1.