The Powerful New Magellan Telescopes

The Magellan Telescopes are a pair of 6.5 m (21.3 ft) diameter optical telescopes located at Las Campanas Observatory in Chile. The two telescopes are named after the astronomer Walter Baade and the philanthropist Landon T. Clay.

First light for the telescopes was on September 15, 2000 for the Baade, and September 7, 2002 for the Clay.

A collaboration between Carnegie Institution for Science, University of Arizona, Harvard University, The University of Michigan and the Massachusetts Institute of Technology built and operate the twin telescopes.
It was named after the sixteenth-century Portuguese explorer Ferdinand Magellan.

In 2013, Clay (Magellan II) was equipped with an adapive secondary mirror called MagAO which allowed it to take the sharpest visible-light images to date, capable of resolving objects 0.02 arcseconds across -- equivalent to a dime 100 miles away.

MagAO was originally intended for the Large Binocular Telescope, but the device was damaged before it could be installed. Project leader Laird Close and his team were able to repair and repurpose the broken mirror for use on Magellan II.

http://en.wikipedia.org/wiki/Magellan_telescopes
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The Giant Magellan Telescope (GMT) is a ground-based extremely large telescope planned for completion in 2020. It will consist of seven 8.4 m (27.6 ft) diameter primary segments, with the resolving power of a 24.5 m (80.4 ft) primary mirror and collecting area equivalent to a 22.0 m (72.2 ft) one. The telescope is expected to have over 5-10 times the light-gathering ability of existing instruments.
Two mirrors are cast and the mountain top has been prepared for construction.
Planned Site
The confirmed location of the telescope will be the Las Campanas Observatory, which is also the site of the
Magellan telescopes, some 115 km (71 mi) noffh-northeast of La Serena, Chile. Much as for previous notable telescopes, the site has been chosen as the new instrument's location because of its outstanding astronomical seeing and clear weather throughout most of the year. Moreover, due to the sparsity of population centers and other favorable geographical conditions, the night sky in most of the surrounding Atacama Desert region is not only free from atmospheric pollution, but in addition it is probably one of the places least affected by light pollution, making the area one of the best spots on Earth for long-term astronomical observation. Major site preparation began with the first blast to level the mountain peak on 23 March 2012.

Unique Design Features
The telescope is unique in that it will use seven of the world's largest mirrors as primary mirror segments, each 8.4 m (27.6 ft) in diameter. These segments will then be arranged with one mirror in the center and the other six arranged symmetrically around it. The challenge in this is that the outer six mirror segments are off-axis, and although identical to each other, are not individually radially symmetrical, necessitating a modification of the usual polishing and testing procedures.

The mirrors are being constructed by the University of Arizona’s Steward Observatory Mirror Lab. The casting of the first mirror, in a rotating furnace, was completed on November 3, 2005, but the grinding and polishing were still going on 6½ years later when the second mirror was cast, on 14 January 2012. A wide array of new optical tests and laboratory infrastructure had to be developed to polish this mirror, as it's coefficient of difficulty is 10 times that of any previous large astronomical mirror. A third segment is scheduled for 2013. Casting uses 20 tons of E6 borosilicate glass from the Ohara Corporation of Japan and takes about 12–13 weeks.

Polishing of the first mirror was completed in November 2012. The second mirror is being processed at the mirror lab, and the third mirror segment will be cast in August of 2013. Materials for the fourth mirror segment have been purchased; that mirror will be cast in late 2014.

The intention is to build seven identical off-axis mirrors, so that a spare is available to substitute for a segment being recoated, a 1–2 week (per segment) process required every 1–2 years.

Although the primary mirror as a whole has a focal ratio (focal length divided by diameter) of f/0.71, the individual segments, being one third that diameter, have a focal ratio of f/2.14. The overall focal ratio is f/8 and the optical prescription is an aplanatic gregorian telescope. The telescope will make use of adaptive optics.

http://en.wikipedia.org/wiki/Giant_Magellan_Telescope