Green light for the construction of the 39-m aperture Extremely Large Telescope (ELT) was given by the Council of the European Southern Observatory (ESO) on Dec 4th, 2014. Procurement of the key elements, especially the optics, the dome and structure and the glass substrates, was soon after initiated by ESO team. Safran-Reosc is proud to have been awarded all the key optical polishing and testing contracts with M4 in 2015, M2 in 2016, M3 and M1 in 2017. This paper reports Safran-Reosc’s work progresses of the last 12 months along these four contracts with their challenges, specifically those related to the mass production of the M1 segments. Keywords: ELT, segmented optics, large optics, optical manufacturing, optical testing, thin glass shell, bonding

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