Blank Canvas: the ELT’s M2 Mirror Blank

This image shows the massive 3-ton blank for the ELT’s secondary mirror. This technological blank has been successfully machined from a slab of the low-expansion ceramic material ZERODUR^Ⓡ into its near-final form by the German company SCHOTT.

M2 will be the largest ever secondary mirror employed on a telescope, as well as the largest convex mirror ever produced. Fabricating this highly convex, aspherical mirror is a considerable challenge — and the result will be a truly remarkable example of pioneering optical engineering. The secondary mirror and its support system — weighing 12 tonnes —  will hang upside-down high above the 39-metre primary mirror.