The U of A mirror lab has for the last 8 years been making the mirrors for the Giant Magellan Telescope which is comprised of seven 8.4 meter mirrors. The center mirror is a normal shaped mirror and the 6 outside mirrors are ground off center so when put together creates a mirror that is 25+ meters across. In 2009 when I spent time in Tucson I used to go to the mirror lab with Dean Ketelsen who was one of the lead opticians there. He retired a few years ago but as things are he still works there because there are very few in the world who can do what he does. When done the GMT will have adaptive optics and so the mirrors will be adjusted often depending on conditions of the sky.
-- Such a long long time to be gone, such a short time to be there.