Talk:List of largest optical reflecting telescopes

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.
 * In the individual telescope articles, HET's collecting area is listed as 77.6 m2, while SALT's is listed as 79 m2. Shouldn't this mean that SALT has a bigger effective aperture?  --Lasunncty (talk) 08:59, 6 August 2018 (UTC)
 * The HET was upgraded in 2015 to increase the effective aperture from the same mirror assembly. This list and the text of the HET article were updated to reflect that, but the HET infobox was not. The infobox data was recently moved to Wikidata, which is a nightmare to navigate, but I think I've managed to fix it. Modest Genius talk 12:23, 6 August 2018 (UTC)

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.

SOAR?
The SOAR telescope has a diameter of 4.1m, not 4.2. Does it still qualify?--Jkru214 07:07, 17 September 2007 (UTC)

LBT vs. Keck
Should the twin mirrors of the LBT be treated as one while the larger Kecks are treated as two? Aside from being in adjacent buildings, what is different between the LBT twins and the Keck twins? 66.218.190.100 (talk) 19:49, 26 August 2008 (UTC)

Yes, LBT is one telescope when used in the combined beam mode. It operates exactly as a 23m diameter telescope with an un-filled aperture. — Preceding unsigned comment added by 140.254.79.232 (talk) 17:04, 11 October 2011 (UTC)

Contradictory list
This list seems to follow its title "List of largest optical reflecting telescopes" at the top. But it then becomes a either a "History of reflector aperture" or simply a "List of notable reflecting telescopes" towards the bottom with a whole series of reflectors that are not "large" at all and ends with what is probably the worlds smallest notable reflector, Newton's first 1.3″ reflector. So the list contradicts its title. It should probably be reduced to existent operation telescopes as cited in this source. Some of this could be spun off to other list "List of notable reflecting telescopes", "History of reflector aperture", or "History of aperture". Fountains of Bryn Mawr (talk) 21:09, 6 April 2009 (UTC)
 * Cleanup of page to remove contradiction with article title. Cut list and article off at two meters since most reference lists stop around that size. The former article can probably have more info spun off to "List of largest telescopes historically " based on the ref here (that ref has noticeable errors). Fountains of Bryn Mawr (talk) 21:40, 8 April 2009 (UTC)
 * I have created List of largest optical telescopes historically from this material. Fountains of Bryn Mawr (talk) 15:19, 16 April 2009 (UTC)
 * The contradiction you speak of has bugged me for some time but I was not sure of the best way to resolve it. What you have done seems like a step in the right direction, and I will now try to incorporate some additional changes. Fotaun (talk) 13:24, 27 April 2009 (UTC)
 * I was thinking of (and may do soon) a few more edits to incorporate your expansion of the list. Expanding this article to include them is a problem because we are still pretty contradictory with the title at the top of the page, lists just can't contain everything. The best way to avoid contradicting this list's title (other than changing it) is to move the material to more appropriate titles. When I moved stuff over to List of largest optical telescopes historically I noticed room for expansion there since an absolute size list kinda misses the story (and it turned out pretty short :/).
 * I would suggest the following:


 * At the "List of largest optical telescopes historically" article create a second table---Table of optical telescope progression historically" and make that a historical list of telescopes by significance, not overall size. With a little ref we can show the historical significance of telescopes such as the Hale 60, etc. Change the title of the first table to "Table of largest optical telescopes historically by overall size".


 * Move other items the don't fit historical and are simply not "large" to the neglected list - List of optical telescopes (and maybe change the title to List of notable optical telescopes). Sub tables could be added there as well like "List of space based optical telescopes".
 * Fountains of Bryn Mawr (talk) 20:25, 28 April 2009 (UTC)
 * I think History of aperture is a worthwhile concept; what is considered "large" has certainly changed over time. The new '20th century telescopes' was intended to build on that concept, but it may be too redundant. Fotaun (talk) 20:08, 5 August 2009 (UTC)
 * rm'ed (again) "Selected large telescopes 6 feet (1.82 m) and below" - it still contradicts the article title, "small" telescopes don't belong on a "List of largest optical reflecting telescopes" by definition. It also suffers from redundancy and scope problems re: WP:SALAT.... space telescopes already have a list List of space telescopes.... "regionally famous telescopes" and "otherwise significant" is just too broad in scope and would result in a never ending list where editors add their POV favorites, and those description parameters contradict "largest optical reflecting telescopes". Some material moved off to List of largest optical telescopes historically.Fountains of Bryn Mawr (talk) 12:18, 13 August 2009 (UTC)

Reverted an edit described as "misc"
Some of that was probably good but wp:Original research, but some of it seemed problematic, and some was simply not correct. Please wp:edit summaries, wp:reliable sources.- sinneed (talk) 17:15, 28 August 2009 (UTC) On review, it wasn't any worse than it was before... so why revert? Article still needs, IMO an application of a sharp editorial hatchet... it's a list. *shrug*- sinneed (talk) 17:42, 28 August 2009 (UTC)

Stem and Leaf
Can anyone explain to me the purpose of the stem and leaf plot? What encyclopedic benefit does it provide? 99.242.102.36 (talk) 06:41, 26 November 2010 (UTC)
 * hmmm... yeah. Its also quite WP:JARGON. Don't see any reason for it per WP:SAL and unless there is some obvious reason to have it looks like it could simply be deleted. Leaving it for now to see if it can be improved or explained. Fountains of Bryn Mawr (talk) 23:20, 14 February 2011 (UTC)

I also agree it is not needed. Since there's been 2 people before me saying this, I am going to just delete it. Yialanliu (talk) 01:21, 25 July 2012 (UTC)

Strehl ratio jargon

 * Without adaptive optics telescopes have Strehl ratios of less than 1% but first generation AO can boost this up to 20–30%.

Moved above to talk because it is 100% WP:JARGON (and its ref dead-ends so no way to check out the claim). Needs work. Fountains of Bryn Mawr (talk) 23:05, 14 February 2011 (UTC)

Top Telescope 2000 and 2010
I find this to be redundant especially since the top table includes the size and year built. In addition to this, the lower table includes the largest telescope every year. Any thoughts on this? Yialanliu (talk) 01:26, 25 July 2012 (UTC)
 * Agreed, it's pretty pointless trivia. The table of the largest historically is all that's needed. PS. new discussions should go at the bottom of the page, see WP:TALKNEW. Modest Genius talk 11:00, 25 July 2012 (UTC)

Is the Large Binocular Telescope the largest?
I moved Large Binocular Telescope down the list from largest because it was moved up by an IP without comment/reason and this is an extremely qualified claim. This abstract describes it as "A unique feature of LBT is that the light from the two primary mirrors can be combined optically in the center of the telescope to produce phased array imaging of an extended field. In practice this extended phased field can be of order 1-arcminute in diameter". I am basing it on the list def exclusion of interferometry, including "phased array" in that, although this list def is not fully expressed. List def could be better written/modified. Other refs. Fountains of Bryn Mawr (talk) 15:55, 11 February 2013 (UTC)
 * I'm pretty sure that the LBT has an incoherent mode, whereby the two mirrors just collect a lot of light and send it to a common instrument (or two copies of the same instrument). By collecting area that does indeed make it the largest - Keck and VLT only have interferometric multi-mirror modes. I don't have a reference to hand though. Modest Genius talk 16:11, 11 February 2013 (UTC)

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different ways to define "largest"
There are at least two different ways to define which telescope is the largest. One is by the light gathering area (which determines the faintest objects that can be seen) and the other is the maximum baseline (which determines the minimum angular resolution). I would like to see both of these numbers listed in the table so that readers could sort by whichever statistic they choose. --Lasunncty (talk) 02:22, 17 March 2016 (UTC)

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 * The science.howstuffworks.com archive is good. The ociw.edu link is now at obs.carnegiescience.edu.  The lbti.as.arizona.edu archive is good.  The gmto.org archive didn't work, but I found another page on that site that had the referenced information.  --Lasunncty (talk) 01:54, 25 May 2017 (UTC)

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 * Found some updated links, and a couple near matches:
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 * The DCT link I found is more up to date than the archived link.
 * --Lasunncty (talk) 09:04, 6 January 2018 (UTC)

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H.E.S.S. Telescope
The largest of High Energy Stereoscopic System telescopes is 28 m in diameter and is a reflecting telescope and isn't on the list. With 28 m, shouldn't it be first? 77.103.237.203 (talk) 17:39, 8 January 2019 (UTC)


 * HESS is a gamma-ray telescope, not an optical telescope. Modest Genius talk 15:56, 9 January 2019 (UTC)

Isn't VLT the largest combined optical telescope, as of 2018?
As of 2018, the VLT appears to have combined the beams of all 4 of their telescopes, and fed it into a single instrument. ESO claims that the equivalent apperture is 16 meters. Doesn't it mean that, as of now, the VLT is the largest working optical telescope? Although they do not share the same mount, the light is still collected in a single instrument. Shouldn't the same mount requirement be dropped? Source by ESO here 80.112.163.52 (talk) 13:45, 2 May 2020 (UTC)


 * It is possible to use all four UTs to feed the optical interferometer, and ESO has done so a few times per year. But >95% of the time they operate as independent telescopes, observing completely different objects with separate instruments. The interferometer mostly operates with the much smaller ATs. There is no incoherent feed for the UTs - it's not possible to use all four telescopes together with a non-interferometric instrument. So describing them as a single telescope would be misleading. In contrast, the LBT mirrors are on a single mount and always observe the same object, and it uses a mix of coherent, incoherent and duplicate-instrument modes. Those are qualitatively different ways of observing. I think the UTs should continue to be four separate entries, but perhaps the list should be clearer that it is excluding interferometric-only modes. Modest Genius talk 11:06, 4 May 2020 (UTC)