Talk:List of largest optical reflecting telescopes

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This may be interesting sometimes [1]

[edit] Hobby Ebberly telescope

I think the diameter of the Hobby Ebberly telescope may be wrong on this page. It is often quoted as being the largest telescope in the Northern Hemisphere. Rnt20 06:17, 14 October 2005 (UTC)

Yes, the mirror diameter is 11 meters, just as the Southern African Large Telescope; however, the design of the telescope optics is such that a maximum of only 9.2 meters of the mirror gets used at any given time. AmberRobot 23 Feb 2006

I believe that the proper way to deal with this is to put the effective area for the spherical mirror telescopes. Just like the HET, SALT is spherical, and therefore has a much smaller effective area. Speaking of SALT, it is now operational, although still in the testing phase. So the top should probably be edited from saying that the first three are not operational.

[edit] Moved from page

I've removed the following text from the page, as it doesn't really fit in with the page (it's meant to be a list, not an article on the history of the lens types). If they are added back, please add them in the appropriate place in the list using footnotes or similar. --Mike Peel 14:26, 31 July 2006 (UTC)

  • Until MMT in 1980s, all large telescopes used a single solid primary mirror whose material internal strength had to be sufficient to limit deformations caused by its own mass flexing while being moved around.
  • The MMT pioneered multiple-mirror technology, but in the end it was possible to build a single large mirror for it, and it was rebuilt and recommissioned in 2002.
  • The MMT also taught telescope makers that an oversized enclosure building (a "dome") is not only very expensive, but collects warm air whose turbulent mixing with the putside atmosphere ("dome seeing") harms overall telescope performance. Thus, all new large telescopes barely fit inside their domes, and those domes are very lightweight structures indeed so that they can quickly cool to night temperatures.
  • At several other new telescopes in the late 1980s, various dynamically computer-controlled support systems (active optics) were developed for thin mirrors too flexible to hold their own shape. The first major telescope commissioned using such was the Nordic Optical Telescope in 1988, which has a) thin mirror (cheap), b) snug fit minimum size dome (cheap), c) alatazimuth mount (cheap), d) big air vents to be opened at night e) adaptive optics, and f) location with excellent seeing conditions, and while it is mere 2.56 m in diameter, it does routinely reach sub-arcsecond angular resolution, which is very close to the diffraction limit of this size telescope.
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