“Extremely” precise
New CNC machine enables highly accurate processing of mirror components for the Extremely Large Telescope (ELT)
Before a telescope mirror can perform its actual function in a telescope, a long and challenging path lies before it. This applies not only to the transport to the place of use, but especially to the many steps during the manufacturing process. After all, high-precision optical components are crucial for the quality of images from distant galaxies – and thus the success of the entire project.
The ESO (European Southern Observatory) Extremely Large Telescope has once again raised the bar for specifications of individual components with its 39-meter main mirror and a sophisticated mirror system. The SCHOTT technology group, which recently received the order for the secondary (M2) and tertiary mirror (M3) of the ELT, is ideally prepared for this super project with its state-of-the-art equipment: A new 5-axis CNC machining center, which has now been completed, will enable ZERODUR® glass-ceramic mirrors to be produced up to five meters in diameter dimension with a not achieved precision.
The ESO (European Southern Observatory) Extremely Large Telescope has once again raised the bar for specifications of individual components with its 39-meter main mirror and a sophisticated mirror system. The SCHOTT technology group, which recently received the order for the secondary (M2) and tertiary mirror (M3) of the ELT, is ideally prepared for this super project with its state-of-the-art equipment: A new 5-axis CNC machining center, which has now been completed, will enable ZERODUR® glass-ceramic mirrors to be produced up to five meters in diameter dimension with a not achieved precision.



Due to the numerous optimizations, the CNC machining center at SCHOTT will offer greater process flexibility in future mirror substrate manufacturing for the ELT. Thomas Werner concludes: “With a second melting tank and the fully-simultaneous CNC machining center for our ZERODUR® glass-ceramic, we are ‘extremely’ well prepared for the ELT project.” After the M4 mirror substrates left the plant in Mainz in 2016, the secondary mirror will be delivered in January 2019 and the M3 mirror in June 2019. ZERODUR® glass-ceramic has a thermal expansion coefficient close to zero and is now used in all major telescope projects.

The optical system of the E-ELT and the role of ZERODUR®