Six years ago, in episode 150, Jochen Liske of ESO told us about the Extremely Large Telescope that is currently being built in Chile. This episode is a continuation (which is why this is a kind of bonus episode labelled as 150.5) in which Thomas Pfrommer tells us about how to control the optical path of this monster telescope: the 39 meter, 798-segment main mirror, plus the four additional mirrors involved in bringing the light to a stable and sharp focus. I recorded this episode mainly to fill in some “gaps” I needed for the book chapter on telescopes.

Here is the paper I read, which triggered this episode: MELT – An optomechanical emulation testbench for ELT wavefront control and phasing strategy. You should read it before you listen. Just kidding (sort of :-)).