ELT secondary mirror blank in the streets of Mainz

Transfer of ELT secondary mirror blank to the SCHOTT 4-metre blank annealing facility in Mainz, Germany in May 2017. The blank was cast out of ZERODUR®, a material originally developed for astronomical telescopes in the late 1960s. Zerodur® has almost no thermal expansion even when subjected to large temperature fluctuations, is highly chemically resistant, and can be polished to a high standard of finish.