“…When it will be operational, the ELT (Extremely Large Telescope) will be the largest optical telescope in the world. 1,2 ESO (European Southern Observatory) has entrusted Safran Reosc with the polishing of all of ELT mirrors, 3,4 notably its primary. M1 is a quasi-parabolic ellipsoid (R = 68.685m, k = −0.996473) that measures 39.3 m in diameter and is segmented in 798 off-axis aspherical mirrors with 133 unique definitions (surface form and geometry).…”