Talk:Optical telescope

two primary types?
I have been cleaning up some of the telescope related articles (Reflecting telescopes, Catadioptric, Cassegrain reflector) (and seeking clarification via the web) and most references I am coming across state that there are "three basic types of telescopes: refractors, reflectors and catadioptrics". Is there a preferred nomenclature? i.e. are there three types (the third being catadioptric?) or are there only two types and a combination of the two (compound telescopes?) I am going to edit this article to fit what seems to be more prevalent but would appreciate any input.Halfblue 13:26, 24 September 2006 (UTC)

Eye_relief - correction for the diagram "Keplerian telescope, schematic"
Look at: http://en.wikipedia.org/wiki/Eyepiece http://en.wikipedia.org/wiki/Eye_relief

The distance between the eye (3) and the eyepiece (2) doesn't have to be equal to the eyepiece focal length "f2" so the diagram: "Keplerian telescope, schematic" Should be corrected. —Preceding unsigned comment added by 212.179.253.187 (talk) 21:00, 2 November 2007 (UTC)

More history?
The following was added to the intro at Telescope. I am moving it here because it seems to deal with specifically Optical telescopes. I am putting it in talk because some of it does not have much to do with telescopes (camera obscura, pinhole lenses, ect.), and it is full of un-cited claims. Fountains of Bryn Mawr (talk) 00:47, 28 January 2008 (UTC)
 * Crystal Balls were used in China and India as lenses (possibly in the form of a camera obscura) to see at a distance as early as 400 BCE. Around 1000 CE, the Arabian astronomer and mathematician, Ibn al-Haytham, expanding and scientifically testing theories of Euclid, Ptolomey, and Aristotle, wrote about both pinhole lenses and concave lenses in his mathematical book on vision. Roger Bacon wrote about combining lenses to see at a distance in the 13th century, as did the 16th Century Italian spectacle maker, Giambattista della Porta (1538-1615), and a host of others.

DigitalC's reversions
I don't understand. We had a big thing about this over at the telescope article, yet he gives me trouble here. 1st, he asked for a reference (deleting a contribution in the process) then when I provided a reference, he changes his stance to "UNDUE" weight. Some people enjoy bothering and vandalising work, but it's not gong to make me quit. Nothing will. I will assume good faith and wait for a discussion to revert my arguement and references. Sincerely, InternetHero (talk) 02:05, 31 July 2008 (UTC)
 * Exactly. The exact same problem that is happening over at telescope is happening now here. Material that is not specifically relevant to the optical telescope will be removed, unless there is a reliable source that mentions the optical telescope . DigitalC (talk) 04:34, 31 July 2008 (UTC)

I don't understand... We have to get another administrator here. This article from the NY-Times relates him. This essay relates him (6-7th paragraph). This relates him. A nice picture. This article relates him. This article mentions him. This article mentions him. I don't care, I'll add all these refrences if I have to. 3 of them are pretty good, and one is from the NY TIMES!!!. I'm gonna go watch Weng Weng do his thang thang now. Good day, InternetGuy. InternetHero (talk) 08:08, 31 July 2008 (UTC)
 * Just because it is from the New York times does not mean it is a good reference. In fact, it isn't a good reference, because it barely mentions al-Haytham's contribution to the telescope. From WP:UNDUE, "Keep in mind that in determining proper weight we consider a viewpoint's prevalence in reliable sources". Even in the NY Times article, there isn't much weight to the assertation that al-Haytham was important to the development of the telescope. Ignoring the input of other editors is disruptive, and can lead to being blocked again. DigitalC (talk) 23:27, 31 July 2008 (UTC)

The whole newspaper article is about him. The category-holder is Al-Haytham. TTT. InternetHero (talk) 01:25, 1 August 2008 (UTC)
 * Yes, but there is only one sentence in the entire article about how his work led to the development of the telescope. - DigitalC (talk) 01:32, 1 August 2008 (UTC)

If you want bulk, that is not my only reference: This essay relates him (6-7th paragraph)., This relates him., This article mentions him., and the This article mentions him. page. Just let me contribute already. If it's not the references, its another thing. Sheesh. InternetHero (talk) 01:48, 1 August 2008 (UTC)
 * I agree, we are going in circles here. I have already discussed those references when you brought them up at Talk:Telescope. DigitalC (talk) 02:09, 1 August 2008 (UTC)

O.K. Obviously we have a dilemma here. I have a number sources of varying degrees, yet it doesn't seem to convince you to give me a right to edit on the article. What are we to do? I tried to compromise. If I am to compromise more, I should just quit Wikipedia altogether. InternetHero (talk) 02:26, 1 August 2008 (UTC)
 * Everyone has the right to edit Wikipedia, but they must follow the policies of Wikipedia when they do edit. You are correct that the sources you have found do not convince me that there should be any further mention of al-Haytham in the article. If you do not understand this, let me know and I can elaborate further on each of the sources. DigitalC (talk) 03:59, 1 August 2008 (UTC)

I have no problem with the article the way it is. InternetHero (talk) 04:00, 1 August 2008 (UTC)

Undue balance
I have removed the below to talk because it is not a synopsis of the summery at history of the telescope (WP:UNDUE). The only source given (Richard Powers) not a reliable source (opinion piece, not a reliable historical text WP:SOURCES). Fountains of Bryn Mawr (talk) 23:47, 19 October 2008 (UTC)

''Studies of properties of lenses and refraction in the Middle Ages by scholars such as Ibn al-Haytham, Robert Grosseteste, and Ibn Sahl laid the groundwork for the development of telescopes. Although there were some recorded instances of pre-17th century Middle Eastern and European opticians&mdash;such as Leonard Digges, Taqi al-Din and others&mdash;creating devices that could have functioned as telescopes.''

I'm not sure why you guys are so eager to remove the one paragraph that's sourced in this article. The complaint above was addressed by the editor who added a bunch of sources to back up the content. It seems to me to be a reasonable short summary of the prehistory of the telescope. How is that undue weight? Dicklyon (talk) 05:16, 25 November 2008 (UTC)
 * It is undue weight because this is an article on the optical telescope, not an article on the History of Optics. Further, if we were to have a summary of History of Optics here, it would have to adequately summarize the article, and not place undue emphasis on certain contributions. There has been much previous discussion on this, which is likely available in the archives/talk pages of Telescope, History of the telescope, as well as here. DigitalC (talk) 05:22, 25 November 2008 (UTC)


 * So why is there a history section at all? It doesn't even talk about Newton or reflectors, just a few random unsourced snippets of history.  And if this article has undergone extensive discussion already, how is it that it's unsourced still?  Seems to me that sourced stuff should generally get priority over unsourced stuff, and that you can argue about balance only when there's enough sourced stuff to worry about. Dicklyon (talk) 05:36, 25 November 2008 (UTC)


 * It has had intense discussion due to the actions of a POV-warrior, inserting the same information into multiple articles. Sourced content, that is relevant to the topic at hand (in this case, the Optical telescope) would be appreciated. Of course, it would have to be directly related to the topic, per WP:OR. As such, any History section here should really be a linked summary of History of the telescope, not History of Optics. DigitalC (talk) 06:09, 25 November 2008 (UTC)


 * I realize that InternetHero has been a pain for a long time, but it looks like he finally managed to find some good sources and write some intelligible sentences that are on topic. Did you read what he wrote and check the source?  Doesn't look at all bad to me; the sources are about optical telescopes and their history (at least the ones I checked online). Dicklyon (talk) 07:05, 25 November 2008 (UTC)


 * I think the appearance of undue balance is due to missing material, not extra. Having a paragraph on history of telescopes is good, starting with the precursors is OK, but then it needs a few more sentences (Newton and reflectors, bigger and bigger, sophisticated optical designs, branch into other fields (radio, gamma ray, etc).  LouScheffer (talk) 11:53, 25 November 2008 (UTC)

The problem with the sourced stuff is that the sources are unreliable and they do not match the general scholarly record (you can't just source stuff, you have to meet WP:RELY and cover all significant views). Optics and the technology of mirrors and lenses did not start in the 10th and 11th centuries and there is a great deal of development after that time. The addition of Leonard Digges, Taqi al-Din, and Giambattista della Porta to a synopsis of History of the telescope is wrong because it is very dubious that they had anything to do with telescopes and Taqi al-Din falls under "very tiny minority viewpoint". Other editions such as "The next big advance was the reflecting telescope of Isaac Newton" is a bit off, the idea had been kicking around before and after Newton. Newton did not originate the reflecting telescope, he was simply the first to get one to work (see Newtonian telescope), and his design was in fact a 100 year dead end. This stuff is sourced, it is simply sourced in its parent articles. I have reworded the section accordingly. Fountains of Bryn Mawr (talk) 15:50, 25 November 2008 (UTC)


 * At this point I believe undue weight has swung the other way. Your first reference specifically states 'in the west' for spectacles, and the second 'History of the telescope', on page 26, credits the Alhazen as the first to study these systematically. LouScheffer (talk) 16:14, 25 November 2008 (UTC)


 * The first source is one of many that seem to agree giving us a general scholarly record POV, see Talk:Telescope for other examples. 'History of the telescope', on page 26, specifically says Alhazen knew of the magnifying effects of glass segments but "did not mention using them as aids to vision". And we seem to be skipping Roger Bacon, which maybe we should, since this is a summery of History of the telescope, not History of optics. Fountains of Bryn Mawr (talk) 17:00, 25 November 2008 (UTC)


 * Since a practical telescope takes both theory and practice, I think at least a sentence of each makes sense. (and the New York Times article, among others, belives the telescope and microscope derive directly from the early work on optics.)  Roger Bacon was also reputed to have a telescope design, so I added him in as well.  I think it's better in general, to include these claims with the caveat that they are not generally accepted.  Otherwise folks think they were improperly ignored and will keep adding them back in.  This way it's their job to find more and better evidence, which is hard for marginal claims.   LouScheffer (talk) 17:09, 25 November 2008 (UTC)

(de-indent) The fact that the first telescope came out of the practical optical applications of spectacle makers and maybe even from children playing with lenses[] means there may be very little "theory" behind its invention. Sources such as Powers are newspaper opinion pieces and "are only reliable for statements as to the opinion of their authors, not for statements of fact" WP:RELY. And this is supposed to be a summery of History of the telescope, not History of optics. HOT does not include Alhazen and Ibn Sahl in its summery. "theory of optics was developed starting in the 10th and 11th" is not supported or supportable by reference (see: History of optics) and again probably did not lead to the first telescope. Alhazen added in context where he is suspected of making a contribution. Prose style should be a history, not description, the descriptions of how a reflecting telescope works should be in "How it works". Netherlands and Germany spectacle making dates to the 16th century. Please do not re-add dubious non summery material such as Roger Bacon, Leonard Digges, Taqi al-Din, and Giambattista della Porta since: they have little to do with historical development - no one knew about them at the time, they were only discovered in writings after the fact, Della Porta may simply be describing bifocals, and Taqi al-Din only has one source an no scholarly discourse. And again we should be following WP:SUMMARY when creating a summery section. Reworded Niccolò Zucchi's contribution since it is another "after the fact" claim (1652). Need to avoid implying that Reber's was the first radio telescope, Jansky's was the first, he did not build it to be a radio telescope, but he used it that way. Fountains of Bryn Mawr (talk) 20:38, 25 November 2008 (UTC)


 * Let's look carefully at InternetHero's re-added paragraph now, and fix it up as necessary if what it states is not exactly verifiable, now that it's more clear that there's no consensus that such content doesn't belong here. I also don't buy the argument that this section has to be a summary of what's in the other main-linked article, though of course if there are conflicts between them we should attempt to resolve those. Dicklyon (talk) 16:46, 27 November 2008 (UTC)
 * A man named O.S. Marshall directly stated that Al-Haythams work in refraction, convex/concave lenses, parabolic mirrors, angles of incidence, atmospheric refraction, and the magnifying properties (both physical and mathematical) initiated the design of the microscope and telescope. In fact, in the last page he credited him with the idea that he could have even made a telescope if he had the time or energy (he was very old at this time).
 * As for Leonard and Taqi, I don't see a website that has been referenced on British television shows is a "minority viewpoint". Muslimheritage.com is a viable reference---one of which Wikipedia's goal is BASED on. Reference: Page 8, last paragraph. Thanks for your time. InternetHero (talk) 16:50, 27 November 2008 (UTC)

It is not Wikipedia policy to "fix" what is not exactly verifiable. In fact it is exactly the opposite (please read Jimmy Wales comments at the policy page). There has been sufficient time to provide reliable references, and so far they have not been forthcoming. There need to be reliable, published source and those "source('s) cited must clearly support the information as it is presented in the article". If this material can not be clearly supported by general scholarly articles on the history of telescopes it should not be included in a summery here. Tiny-minority views like, say Taqi al-Din is covered in the article devoted to the subject--> History of the telescope and Taqi al-Din - WP:SOURCES. Fountains of Bryn Mawr (talk) 03:34, 29 November 2008 (UTC)


 * OK, if the issue is verifiability, we can work with that. I have to say I find it remarkable that InternetHero was able to write one version with complete English sentences and punctutation, and has then gone off and written two worse versions, actually getting remarkably worse in each attempt; maybe he had a temporary ghost writer.  Anyway, I might look into his refs some more, but I'm not interested in trying to fight his fight, just wanted to point out that his stuff shouldn't be removed for reasons other than what are stated, as appeared to be the case recently. Dicklyon (talk) 08:13, 29 November 2008 (UTC)
 * The issue is not simply verifiability. It is also an issue of undue weight and an issue of harmonization with the article it is summarizing. If there is to be a history section in this article, it needs to be a balanced summary of History of the telescope (obviously not incorporating non-optical telescopes). Just because something is verifiable does not mean it should be incorporated into the article. DigitalC (talk) 00:44, 30 November 2008 (UTC)


 * Of course, but if it's verifiable and relevant, the burden is on one who wants to remove it. Dicklyon (talk) 01:00, 30 November 2008 (UTC)


 * Hi, I started out just researching for school, but I didn't know the muslims made the things you need for the telescope.. we should add them since I didn't even know. My teacher didn't mention them... I'm going to make a GREAT project guys. —Preceding unsigned comment added by Boomshakalakaboom (talk • contribs) 01:40, 30 November 2008 (UTC)

History de-construction - please comment
Here's my re-written introduction. Let's try commenting/correcting/etc., on smaller units than wholesale reversions. Also, feel free to leave your approve/disapprove on each sentence/section so we can see if we have any concensus here. Thanks, LouScheffer (talk) 05:16, 30 November 2008 (UTC)

Telescopes are based on the science of optics and the technology of mirrors and lenses.


 * This seems rather evident, but the book 'History of the Telescope' could be used if needed. Note that although a primitive telescope could perhaps be built without the use of optics, almost every telescope after the very first assuredly used both optic and lens/mirror technology.  Also, this section should give at least some idea of where telescopes sit in the history of science adn technology, IMO.  Optics and lenses/mirrors are clear precursors, radio, etc. telescopes are successors, and the microscope is a very similar and contemporary development.

The scientific study of optics was developed starting in the 10th and 11th centuries by scholars such as Alhazen[1][2] and Ibn Sahl[3] and practical lens-crafting technology was developed by the spectacle makers of 13th century Italy and Germany.[1][4]


 * Seems well supported by the sources cited.

Despite some earlier claims[5] the first historically accepted telescopes appear in the Netherlands in 1608.


 * Pushed the earlier claims to a footnote, so they do not interrupt the flow, but they are still present so a new contributor will not be tempted to add them back

Their invention is credited to three individuals: Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, and Jacob Metius of Alkmaar[6].


 * I've seen no argument on these points

Galileo greatly improved upon these designs the following year and is generally credited with being the first to use a telescope for astronomical purposes. Galileo's telescope used Hans Lippershey's design of a convex objective lens and a concave eye lens and this design has come to be called a Galilean telescope.


 * Use in viewfinders and binoculars not relevent here.

Later on, Johannes Kepler described the optics of lenses[7], including a new kind of astronomical telescope with two convex lenses, often called the Keplerian Telescope.


 * Note that Kepler's optics did not include refraction, which earlier works did.

The reflecting telescope uses a curved mirror in place of the objective lens, offering several technical advantages.[8]


 * Pushed advantages to the footnotes.

Again there are earlier claims[9], but Isaac Newton made the first practical design (the Newtonian telescope) in 1669.


 * Pushed earlier dead ends to footnotes. A reader looking here for a summary does not need to see these dead ends, but I think they should remain in some form to assure people these claims were not forgotten, just not on the main path of development.

Other important developments in reflecting telescopes were John Hadley's production of larger paraboloidal mirrors, and long-lasting and highly reflective coatings.[10]


 * Nearly straight from the page History of the telescope. Pushed coating details to footnote.

This path lead to the main optical telescopes of modern times, which use huge mirrors and sophisticated designs to optimize light gathering power and field of view while minimizing off-axis optical aberrations.


 * I've seen no objections to this so far.

In the mid 20th century, telescopes branched from the optical into many other fields. A radio telescope was constructed by Grote Reber in 1937, and many types of telescopes were developed for a wide range of wavelengths from radio, to gamma-rays.


 * I think we can leave out the words 'purpose-built'. That's what a telescope is - a gadget for looking for stuff in the heavens.  Even if other stuff was used to first detect that radiation was falling on the Earth, it's not a telescope unless it was designed for that purpose (Otherwise, to be consistent, the telescopes of the 1600s were not the first either, since the eyes of animals had been used to sight astronomical phenomina for millions if not billions of years before)


 * Some tweaks:
 * ''Telescopes are based on the science of optics and the technology of mirrors and lenses.

''
 * That’s a description, not a history, and it seems like the first "telescopes" were not based on science at all, they were discovered by happenstance.
 * But the description has an explicit connection to history - the pre-requisites must occur first, before the telescope can be developed. And even if the very first telescopes were developed by happenstance (and I've see no reliable sources on this, just speculation), then improving the initial design, and all the telescopes since, have used the ideas of optics.


 * The scientific study of optics was developed starting in the 10th and 11th centuries by scholars such as Alhazen and Ibn Sahl and practical lens-crafting technology was developed by the spectacle makers of 13th century Italy and Germany. 


 * That part is totally inaccurate. "scientific study of optics" as cited in the Henry C. King source started at least with Euclid and Ptolemy, "starting in the 10th and 11th centuries" can not be supported by source Powers (see previous reasons), and such a statement is not supported by the larger scholarly discourse (see previous references).
 * I disagree with this reading. Page 26 of King states "Euclid was the first to write about the refraction and reflection of light and mentioned that light travelled in straight lines.  Ptolemy's knowledge was equally restricted and just a summary of the ideas of his predecessors.  Alhazen, an Arabian writer of the 10th to 11th centuries, was the first to experiment with different media with the hopes of finding a working theory of reflection and refraction".  Experimentation with the goal of finding a theory is the heart and soul of the scientific method, and it seems that Alhazen is the first to try this.  "In a 1572 translation of Alhazen's work, there is also reference to plane, spherical, and parabolic mirrors."  This is definitely optics not covered by the ancients. LouScheffer (talk) 05:13, 1 December 2008 (UTC)


 * Please note, we have more than King as a source on this, and we need to match the general scholarly record, not just one source. Euclid, (or somebody) wrote the book Catoptrics, which concerns the mathematical theory of mirrors, particularly the images formed in plane and spherical concave mirrors. So he had more to do with optics than just light traveling in straight lines. Fountains of Bryn Mawr (talk) 15:23, 2 December 2008 (UTC)


 * That still doesn't support the claim that the study of optics started in the 10th and 11th centuries. DigitalC (talk) 06:41, 1 December 2008 (UTC)
 * But the claim was not the study of optics, which did start earlier, though in a rather meager and unsatisfactory form, but the scientific study of optics, which by all accounts did indeed start in the 10th and 11th centuries (any references for an earlier start would be appreciated). LouScheffer (talk) 13:37, 1 December 2008 (UTC)
 * The problem is that it is original research to conclude that the scientific study of optics started in the 10th and 11th centuries. That is NOT a claim supported by the source, it is a conclusion you have arrived at after reading the source. DigitalC (talk) 00:54, 2 December 2008 (UTC)
 * I think this is a stretch to call this OR. In elementary school, we learn that the basis of the scientific method is experiments to confirm/contradict a hypothesis.  This is exactly what the text states Alhazen was the first to do.  Other sources confirm this view - for example see the book "Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Middle Ages and the Renaissance: Middle Ages and the Renaissance", by Robert E. Krebs.  "He was one of the first to use a scientific method that involved establishing relationships between one's observations, proposing hypotheses, and verifying one's assumptions by experimentation."  Also, not on this exact point, but germane to the whole discussion, the same text states of Alhazen's work "Understanding both refraction and reflection were important in the development of astronomical instruments such as the telescope." LouScheffer (talk) 02:07, 2 December 2008 (UTC)


 * The scientific study of optics was developed starting in the 10th and 11th centuries
 * There is an OR problem, "you must cite reliable sources that are directly related to the topic of the article, and that directly support the information as it is presented." the sources are in one case unreliable and in the other does not directly support the information as it is presented.
 * See the above quote, that *directly* states this. LouScheffer (talk) 16:40, 2 December 2008 (UTC)
 * A second problem with what IH and others are adding is that their edits are totally irrelevant to the topic and/or offer no reference that it is relevant to the topic. I have chassed down a whole series of their edits (just see my waste of time record) and they continual add edits stating "XXXXXXX was a figure in XXXXXXX invention/development" not "XXXXXXX was the irrelevant figure in XXXXXXX development or its inventor". This addition is one of those edits; it simply "spams" a name in another article. This is POV editing since it ignores all the other, and probably more relevant, figures or developments. So we have the problem here of ignoring all the more irrelevant people and developments that came before and after Alhazen and Ibn Sahl, ignoring the History of scientific method, and thereby push two figures forward in another article. There is a concept in WP:NPOV, Let the facts speak for themselves. The example given there is moralizing but it is applicable here. We should not be making blanket statements (especially unsupported ones) here, just present the facts relevant to a short a summery, and let the reader decide.Fountains of Bryn Mawr (talk) 14:57, 2 December 2008 (UTC)
 * But as Commander Doolittle explains to the intelligent bomb in Dark Star, a concept can be valid no matter where it originates. Although a reference to Alhazan  and/or Ibn Sahl might be irrelevant in many places, it is very relevant here.  Without pre-cursors and successors, IMO, a history is meager and unsatisfactory - I want to know that lenses were available because of the eyeglass industry, and that optics had already been studied as a science at the time of the telescope's invention.  Likewise, I want to know that other kinds of telescopes came later, perhaps inspired by the scientific discoveries of the optical telescopes.  LouScheffer (talk) 16:40, 2 December 2008 (UTC)
 * IMO is where the problem lies (we all have opinions). Wikipedia articles are not created from opinion, they are created from other boiled down references and their predominance in the scholarly discourse. There are clear references as to the balance of all these people and developments in the history of the telescope. Adding Alhazan and/or Ibn Sahl here is a skew of that balance (WP:UNDUE). Alhazan  and Ibn Sahl and the eyeglass industry and optical science are covered in History of the telescope, the section this article is a summery of. Summary style gives clear guidelines re: keeping summary articles and detailed articles synchronized and avoiding of POV forks. Fountains of Bryn Mawr (talk) 18:46, 2 December 2008 (UTC)


 * Despite some earlier claims


 * These really are not "claims", and again, this is a summery and we are treading into WP:UNDUE and getting beyond a summery. (see previous reasons).
 * No, the claims are made by various folks (not the inventors), that so-and-so invented the telescope. I agree thees are based on fragmentary evidence, but still feel it's better to mention and dismiss them, rather than leave it out entirely.  Four words and a footnote are not too much emphasis, in my opinion.  LouScheffer (talk) 05:13, 1 December 2008 (UTC)


 * soon after the optically-similar microscope


 * Needs some citations that the microscopes invention had some bearing on the telescopes invention.
 * Reasonable. They were invented by many of the same people, using the same technology of lenses. LouScheffer (talk) 05:13, 1 December 2008 (UTC)


 * In the mid 20th century, telescopes branched from the optical into many other fields. A radio telescope was constructed by Grote Reber in 1937, and many types of telescopes were developed for a wide range of wavelengths from radio, to gamma-rays.


 * This has many problems so I have RM'ed it to talk. The paragraph is probably not needed since this is a history of optical telescopes. Yes, "A radio telescope was constructed by Grote Reber in 1937" - and this means what?? Did he invent it? no. Was it the first radio telescope? no. Jansky's antenna was the first "gadget for looking for stuff in the heavens" in the radio frequency. In fact he mapped the milky way with it.


 * Other edits made for clarity. Fountains of Bryn Mawr (talk) 19:22, 30 November 2008 (UTC)


 * Just an FYI, have a look at THE INVENTION OF THE DUTCH TELESCOPE. ITS ORIGIN AND IMPACT ON SCIENCE, CULTURE AND SOCIETY, 1550-1650. The paper session synopsis topics lead to some ideas for additions at History of the telescope and may be of interest here.


 * Mark Smith, University of Missouri ALHACEN AND KEPLER AND THE ORIGINS OF MODERN LENS-THEORY "Alhacen has generally been credited with having laid the theoretical and mathematical foundations for the development of modern optics one of whose major steps lay in the invention and perfection of such optical devices as the telescope. While this interpretation of Alhacen’s role in the evolution of modern optics is not implausible on its face, I will argue against it on the basis of a close comparison between Kepler’s analysis of spherical lenses and their focal property and Alhacen’s analysis of refraction in book 7 of the De aspectibus. In the process, I will show that none of the truly creative, or “modern,” elements of Kepler’s analysis are to be found in Alhacen’s account of refraction."


 * Rolf Willach Independent Scholar, Switzerland " Developement of the lens and spectacles - "It also becomes clear that the inventions discussed here were made possible only by practical experiments, insights made by real chance and an intensive interaction between the prevailing cultural and political evolutions in old Europe".


 * Fountains of Bryn Mawr (talk) 23:44, 1 December 2008 (UTC)

Della Porta and first compound optics
From the Max Planck Institute book (Inside the Camera Obscura – Optics and Art under the Spell of the Projected Image Max Planck Institute for the History of Science, 2007, PREPRINT 333, Wolfgang Lefèvre (ed.), p. 42) on the camera obscura:

Neapolitan magician and dramatist Giambattista della Porta first published his Natural Magic in 1558. This contained a short description of the camera obscura, describing both a pinhole camera, and a camera obscura making use of a concave mirror. The second, vastly amplified edition of the Natural Magic, published in 1589 included a much expanded discussion of the camera obscura, including a more sophisticated system that combined a biconvex lens with a concave mirror to produce an upright image.

So it's the first compound optics, not the first telescope. I added this to the article LouScheffer (talk) 00:19, 5 December 2008 (UTC)


 * Its referenced, but what does it have to do with Optical telescopes? Needs a reference that this has some relevance to the history of the telescope.Fountains of Bryn Mawr (talk) 00:50, 5 December 2008 (UTC)


 * Telescopes are compound optical devices, containing at least 2 mirrors and/or lenses. So using two lenses in tandem, as opposed to the simple magnifying glasses used much earler, is a critical step.  As it says in Plant Microtechnique and Microscopy,  Steven E. Ruzin, Published by Oxford University Press, 1999 ISBN 0195089561, 9780195089561, p. 9-10 (this is a history of the microscope, but mentions the strong similarity with the telescope and mentions almost all the same people, since the two devices are so similar.)  You can verify these quotes on line using (for example) the Amazon "search within the book" feature, which allows you to look at a few pages - search for "della".

"'Placing a magnifier between the observer and the object is a relatively ancient human invention. What was novel, and critically important, was the coupling of two magnifying lenses to increase the magnification many-fold over single magnifying lenses."
 * In the above sentence Ruzin is specifically talking about the microscope, but he later is more explicit about the application to telescopes:

"'The direct descendants of della Portas' tandem magnifiers are the microscope and the telescope - now known as 'compound optical devices'."
 * LouScheffer (talk) 14:13, 5 December 2008 (UTC)


 * The problem is stating (as we would be if we dropped in such an addition to a short summery) that della Porta a)Combined two lenses in tandem (if he made bifocals then he did not), and b)That there are a substantial number of reliable sources that say this had relevance to the invention of the telescope (I have not seen that). Lack of a clear historical record/unified opinion in sources mean this should be left out of a summery section (WP:SYNTH. Fountains of Bryn Mawr (talk) 17:00, 6 December 2008 (UTC)


 * The quoted passage above talks about using a two lens system for creating an upright image, so it's not bifocals - it's two in tandem. LouScheffer (talk) 18:03, 6 December 2008 (UTC)


 * A "biconvex lens with a concave mirror" would be a mirror magnifying system (for looking at small objects), unrelated to the telescope. And its citation would have little relevance to a summery, unless it is backed up by being in the larger scholarly record, which it is not. Fountains of Bryn Mawr (talk) 07:25, 7 December 2008 (UTC)


 * There's a good analysis in this book. The title of della Porta's work suggests a telescope, but the details are too obscure to conclude that he made one.  Still, it seems to worth a mention. Dicklyon (talk) 08:33, 7 December 2008 (UTC)


 * It is a worthy a mention, and is covered in {History of the telescope]], where it has context. That could be expanded. 75.196.223.42 (talk) 17:05, 7 December 2008 (UTC)

Wrong section/article
The following section is a description of devices/performance and is redundant to those section covering that topic. They do not belong in history. Parts of it (if referenced) could be integrated into "How it works" or related subsections.

''The resolution of Earth-bound telescopes is determined by seeing and not the diffraction limit. One way around this problem is a space based telescope such as the Hubble space telescope. However, space telescope are extremely expensive and of limited size, so adaptive optics for ground-based telescopes has been developed as well. Other recent advances include segmented mirrors to allow larger diameters and active optics to compensate for gravitational deformation.''

The following section has to do with the word "Telescope" and is already covered in the article Telescope. Radio, gamma ray, neutrinos, cosmic rays, and gravitational waves have nothing to do with Optical telescopes. The material on the derivations and usage of the word "Telescope" could (if referenced) could be integrated to expand the "Telescope" article.

''Until the mid 20th century, all telescopes were optical, and were called simply 'telescopes'. However, starting with the radio telescope, new devices to record emanations of different forms from the heavens were called telescopes as well. Now the phrase 'optical telescope' (a retronym) is used for a telescope that gathers visible light, to distinguish it from telescopes of other types, ranging from other electromagnetic bands (radio through gamma ray) as well as other forms such as neutrinos, cosmic rays, and gravitational waves.''

Fountains of Bryn Mawr (talk) 00:43, 5 December 2008 (UTC)

Versions of history section
Should a history section of a specific device such as telescope discuss, even briefly, precursors, successors, and the some of the whys? Or is this unneeded duplication of information that's appropriate in the ''history of the telescope' article?

This version is preferred by Fountains of Bryn Mawr (talk):

"The first historically recorded devices that came to be called telescopes were refracting telescopes that appeared in the Netherlands in 1608. Their invention is credited to three individuals: Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, and Jacob Metius of Alkmaar."

"Galileo greatly improved upon these designs the following year and is generally credited with being the first to use a telescope for astronomical purposes. Galileo's telescope used Hans Lippershey's design of a convex objective lens and a concave eye lens and this design has come to be called a Galilean telescope. Johannes Kepler proposed an improvement on the design that used a convex eyepiece, often called the Keplerian Telescope."

"The theoretical advantages of the reflecting telescope, that uses a curved mirror in place of the objective lens, were known almost from the invention of the refracting telescope, but Isaac Newton has been generally credited with constructing the first practical reflecting telescopes, the Newtonian telescope, in 1669. Other important developments in reflecting telescopes were John Hadley's production of larger paraboloidal speculum metal mirrors over 100 years later, silver coated glass mirrors in the 19th century, and long-lasting aluminum coatings in the 20th century. This path lead to the main optical telescopes of modern times, which use huge mirrors and sophisticated designs to optimize light gathering power and field of view while minimizing off-axis optical aberrations. The last few decades have sen the introduction of adaptive optics, segmented mirrors, and even space based optical telescopes."

Add your comment here: *Prefer this one, Fountains of Bryn Mawr (talk) (This is not my comment or signature. Fountains of Bryn Mawr (talk) 16:32, 7 December 2008 (UTC))
 * [[Image:Octagon-warning.png|left|30px| ]]PLEASE NOTE This is NOT "my version", preferred or otherwise. It is an amalgamation of mine and LouScheffer version after some ...errr... vigorous editing. Although I appreciate LouScheffer's trying to organize the discussion we should avoid putting words into other editors mouths (namely mine). My preferred versions can be found in the edit history or in this talk addition. Fountains of Bryn Mawr (talk) 16:32, 7 December 2008 (UTC)

- This version is preferred by LouScheffer (talk):

Telescopes (and the optically similar microscopes) are based on the science of optics and the technology of mirrors and lenses, and the history of the telescope is interwined with advances in these fields. Crude optics and crude lenses had been known since antiquity, but the scientific study of optics started in the 10th and 11th centuries by scholars such as Alhazen and Ibn Sahl. Lenses were independently developed for the purposed of making spectacles by the artisans of 13th century Italy and Germany. . The combination of two lenses in a single device (compound optics) was first described in a camera obscura by Giambattista della Porta in 1589 and the telescope and microscope soon followed. Although there is fragmentary evidence for earlier designs the first historically accepted telescopes appear in the Netherlands in 1608. The invention of the telescope is generally credited to three individuals: Hans Lippershey and Zacharias Janssen of Middelburg (who also invented the microscope), and Jacob Metius of Alkmaar.

"Galileo greatly improved upon these designs the following year and is generally credited with being the first to use a telescope for astronomical purposes. Galileo's telescope used Hans Lippershey's design of a convex objective lens and a concave eye lens and this design has come to be called a Galilean telescope. Johannes Kepler proposed an improvement on the design that used a convex eyepiece, often called the Keplerian Telescope."

"The theoretical advantages of the reflecting telescope, which uses a curved mirror in place of the objective lens, were known almost from the invention of the refracting telescope, but Isaac Newton has been generally credited with constructing the first practical example, the Newtonian telescope, in 1669. Other important developments in reflecting telescopes were John Hadley's production of larger paraboloidal speculum metal mirrors over 100 years later, silver coated glass mirrors in the 19th century, and long-lasting aluminum coatings in the 20th century. This path lead to the main optical telescopes of modern times, which use huge mirrors and sophisticated designs to optimize light gathering power and field of view while minimizing off-axis optical aberrations."

"The resolution of Earth-bound telescopes is determined by seeing and not the diffraction limit One way around this problem is a space based telescope such as the Hubble. However, space telescope are extremely expensive and of limited size, so adaptive optics for ground-based telescopes has been developed as well .  Other recent advances include segmented mirrors to allow larger diameters and active optics to compensate for gravitational deformation."

Until the mid 20th century, all telescopes were optical, and were called simply 'telescopes'. However, starting with the radio telescope, new devices to record emanations of different forms from the heavens were called telescopes as well. Now the phrase 'optical telescope' (a retronym) is used for a telescope that gathers visible light, to distinguish it from telescopes of other types, ranging from other electromagnetic bands (radio through gamma ray) as well as other forms such as neutrinos, cosmic rays, and gravitational waves.

Add your comment here:
 * Prefer this one, LouScheffer (talk)


 * I too prefer Lou's version. The brief mention of Alhazen and Ibn Sahl is useful and informative, and will make it easier to control those editors who want to say too much about them.  The stuff about modern telescopes is useful, too, but I'd like to see a source or two there. Dicklyon (talk) 06:51, 6 December 2008 (UTC)
 * I added references for the second to last paragraph; still working on the last one. LouScheffer (talk) 14:27, 6 December 2008 (UTC)


 * The problem with the first paragraph additions re:precursors to the telescope added by LouScheffer et-al is it is for the most part made up from sources not directly related to the history of the telescope. And the History of the telescope articles I have found so far do not explicitly reach the same conclusion. This makes the version WP:OR by synthisis. So it is not enough to simply cite sources, "Article statements generally should not rely on unclear or inconsistent passages nor on passing comments. Passages open to interpretation should be precisely cited or avoided. A summary of extensive discussion should reflect the conclusions of the source's author(s). Drawing conclusions not evident in the reference is original research regardless of the type of source. It is important that references be cited in context and on topic" (WP:OR-Using sources). So we should not be making blanket statements in a summery section that are only supportable by citing disparate sources. If we are saying the passage is open to interpretation in a discussion such as this then the additions should be avoided here and expanded on in History of the telescope. Fountains of Bryn Mawr (talk) 16:19, 6 December 2008 (UTC). The last two paragraphs added by LouScheffer would be an opinion on prose style. I see no real problems with them other then the relevance of where they are added as I have cited above. Fountains of Bryn Mawr (talk) 16:45, 6 December 2008 (UTC)
 * Note the American Institute of Physics thinks early optics are relevent.   LouScheffer (talk) 18:06, 6 December 2008 (UTC)


 * One not very reliable source is not going to get us very far (as in no author, no footnotes, non-Academic and non-peer-reviewed publication). And even that source does not support the claim implied here since it does not make a direct connect between Alhazen and the invention of the telescope. It states the 300 year disconnect and the lenses development via the spectacle industry as the predecessor to invention. The inclusion of Alhazen at aip.org may simply mirroring Wikipedia. It looks like they used The Galileo project as a source since they barrowed some graphics from them. The Galileo project is a much better source since it has an author, researchers, and extensive footnotes. They do not make a direct connect between Alhazen and Ibn Sahl and the invention of the telescope. Fred Watson (page 55) in Stargazer does not make this connection (but does give Alhazen credit in influencing the later reflecting telescope re:copies of Alhazen's book may have been in Gregory's library). Henry C. King in The History of the Telescope does not make an Alhazen and Ibn Sahl only connection, but follows a progression of optical thinking and dead ends  There are sources cited that (Lindberg, David C. (1996), Roger Bacon and the Origins of Perspectiva in the Middle Ages, Clarendon Press) that Alhazen had an influence on Roger Bacon and Johannes Kepler, but this does not connect to the invention of the telescope since nether Roger Bacon nor Johannes Kepler invent it.


 * Other sources:
 * An Acre of Glass By Jack B. Zirker Follows from spectacles.
 * The Telescope By Geoff Andersen Fuzzy records and attribution to Lippershey
 * SIDEREUS NUNCIUS OR THE SIDEREAL MESSENGER By GALILEO AUTOR GALILEI, ALBERT follows the invention from spectacles.
 * Renaissance Vision from Spectacles to Telescopes By Vincent Ilardi, Follows from spectacles and states "Optical theory had nothing to do with the invention (of spectacles)" and elaborates on page 28 how "writings" from "learned circles" from Alhazen down were so incorrect on their theories of vision as to be totally useless to opticians.


 * Fountains of Bryn Mawr (talk) 02:56, 7 December 2008 (UTC)


 * Note that the source is published by a reputable source (AIP), has named authors, has some of the foremost authorities as peer reviewers, and does indeed contain references and further sources. It's probably more reputable than any other source used so far (details are below).   LouScheffer (talk) 17:18, 7 December 2008 (UTC)

-

Is this the best way to resolve the dispute?
Wikipedia does not have different people's versions of articles it is meant to be a collaborative effort. The intention is to produce the best article possible by using the input and ideas of several people.

There do not seem to be any important differences of principle between the two versions (if there are then it is these that should be the subject of the RFC) so why not try to get the best of both by merging them? Martin Hogbin (talk) 15:10, 6 December 2008 (UTC)


 * I've asked for more comments since the process is not converging. If you check the history, there have been many, many passes of adding the additional information in, then another editor taking them out.  Since only a few folsk have been weighing in (see the long discussions above), and some of the differences seemed almost philosophical, it seemed a good idea (to me, anyway) to get some more opinions.  Hence the request for comments.  Thanks, LouScheffer (talk) 15:55, 6 December 2008 (UTC)


 * Just an FYI, This discussion is already on-going at Talk:Telescope. As to difference, I have left comments in the section above. The jist is, the summery of history has to match the general histories found in sources directly related to the history of the telescope. It is fine and dandy to put together unique and interesting items from history people may not be aware of in some forums, but it is not ok in Wikipedia. The best way to solve a dispute like this is to follow guidelines. Fountains of Bryn Mawr (talk) 16:39, 6 December 2008 (UTC)


 * I do not think that LouScheffer is engaging in OR. WP is not intended to be a cut-and-paste encylcopedia.


 * I would suggest that LouScheffer's version is the better starting point for a version that is acceptable for all. Martin Hogbin (talk) 18:20, 6 December 2008 (UTC)


 * Actualy WP is intended to be a "cut-and-paste encylcopedia" since "wikipedia articles should rely mainly on published reliable secondary sources and, to a lesser extent, on tertiary sources" (WP:PSTS). You avoid plagiarism but you don't make up new versions of history, you quote the ones already existent. Fountains of Bryn Mawr (talk) 00:35, 7 December 2008 (UTC)


 * The discussion at Talk:Telescope seems largely irrelevant, since it's not the history article being summarized. But it is clear that there are many good sources that discuss Alhazen in connection with the telescope, including this paper and many books.  Dicklyon (talk) 00:57, 7 December 2008 (UTC)


 * The American Institute of Physics also thinks the optics of Alhazan may be associated with the telescope in the article The first telescopes. And how can you leave out the guy who first describes a parabolic mirror?  LouScheffer (talk) 01:08, 7 December 2008 (UTC)


 * This gets us to the optical thinking that gets us to reflecting telescopes. This is not very useful since it is a not a Google book search "about a subject" (History of the telescope) so the book hits have a POV, although it does hit citations that get us to a reflecting telescope. This is simply an unreliable source by definition. So we have some influence on the invention of the reflecting telescope cited but no citations that the telescope's invention was influenced by Alhazan and one big ol' reliable source that Alhazen and optical theory had nothing to do with the invention of the telescope. BTW I did generate a version where we cite Alhazen's specifically referenced cotributions (based on "give them the facts, don't tell them what to think") but that is lost in the history of editing. Fountains of Bryn Mawr (talk) 03:26, 7 December 2008 (UTC)
 * Why do you say the article on the history of the telescope by the American Institute of physics is unreliable? Next, your big ol' reliable source is talking about the invention of lenses, not the telescope.  Finally, although you can certainly make the argument that optics was not needed for the invention of the first telescope, we are discussing history of the telescope, not history of the invention of the first telescope.  I'd be quite surprised if you can find a reference arguing that optics is not relevent to the development of telescopes in general.
 * "Reliable sources" are defined by Reliable sources. In this case we have an unsigned web page with no footnotes that has no verification as to whether it is peer-reviewed or even well-regarded. Vincent Ilardi actually covers the invention from Spectacles to Telescopes. Spectacle lenses are cited by everyone as the step that lead to the telescope. Optics is "relevant to the development of telescopes in general" but we need to cite that in context specifically and not make blanket poorly referenced and/or unbalanced statements about any one historical figures contribution. Fountains of Bryn Mawr (talk) 07:13, 7 December 2008 (UTC)
 * Fountains of Bryn Mawr, I do not accept your point about WP being cut-and-paste, I am sure this was never the intention, however, I do take your point about early optical theory having nothing to do with the invention of the telescope, although others may have a different view in this. Could we rewrite the first paragraph to talk about early optics but reduce the connection between it and the invention of spectacles and the telescope? Martin Hogbin (talk) 10:03, 7 December 2008 (UTC)


 * How about starting: 'Crude optics and crude lenses have been known since antiquity, and the scientific study of optics started in the 10th and 11th centuries by scholars such as Alhazen and Ibn Sahl. Lenses were independently developed for the purposed of making spectacles in 13th century Italy and Germany'. Martin Hogbin (talk) 10:11, 7 December 2008 (UTC)
 * I think this is good - I'll add it in.  LouScheffer (talk) 14:06, 7 December 2008 (UTC)
 * It fails WP:V. We don't have a source stating that the scientific study of optics started in the 10th and 11th centuries by scholar such as Alhazen and Ibn Sahl. Further, it is off topic to the article, which is optical telescope, not optics. DigitalC (talk) 00:30, 9 December 2008 (UTC)
 * King, page 26: "Euclid was the first to write about the refraction and reflection of light and mentioned that light travelled in straight lines. Ptolemy's knowledge was equally restricted and just a summary of the ideas of his predecessors. Alhazen, an Arabian writer of the 10th to 11th centuries, was the first to experiment with different media with the hopes of finding a working theory of reflection and refraction", plus many more descriptions of his experiments and theories. LouScheffer (talk) 01:02, 9 December 2008 (UTC)
 * I don't feel that that statement verifies the text in question. In fact, to me it states the opposite, that Euclid studied optics earlier. We should follow the sources, and try to find one that explicitly states what we are stating. DigitalC (talk) 03:14, 9 December 2008 (UTC)
 * Euclid was earlier, but there is no evidence he used the scientific method (in particular, trying experiments and discarding theories that do not agree with them. On the other hand, this article about Alhazan PORTRAITS OF SCIENCE: A Polymath in the 10th Century from Science, one of the A+ ranked journals, contains the following quotes:  "But his work in optics was no less revolutionary. He changed the meaning of the term optics, and established experiments as the norm of proof in the field."  and "He also discovered spherical aberration, and gave the correct explanation of the moon's light. Henceforth, experimental control was viewed not only as a general practice of investigation but as the norm of proof in optics, and more generally in physics."
 * Just because it's on the web doesn't mean it's unreliable. The American Institute of Physics (home page) is an organization that has 10 different physics societies as members.  It publishes a number of peer-reviewed journals, and popular magazine such as Physics Today.  There are credits for these web pages and an explicit list of reviewers (David DeVorkin, Owen Gingerich, Michael Hoskin and Robert W. Smith).  Prof. Gingerich, in particular, has explicit expertise in the history of astronomy.  Prof. Hoskin is the editor of Journal for the History of Astronomy.   There is also a list of further reading and web resources.  To me, this seems to offer better reliability than most books... LouScheffer (talk) 13:26, 7 December 2008 (UTC)

(de-indent) We already have some established historical summaries at Lens (optics), History of the telescope, and History of optics plus what is predominately referenced in the scholarly record. That would give us the following:

''The lens and the properties of refracting and reflecting light had been known since antiquity. Optical theory was developed by ancient Greek and Indian philosophers, expanded on in the medieval Islamic world, and had reached a significantly advanced state in early modern Europe. Concurrent with thoretical developement was the practicle developement of lens manufacture for spectacles, first in Venice and Florence in the thirteenth century , and later in the spectacle making centers in both the Netherlands and Germany. It is in the Netherlands in 1608 where the first recorded optical telescopes (refracting telescopes) appeared. The invention is credited to the spectacle makers Hans Lippershey and Zacharias Janssenin Middelburg, and the instrument-maker and optician Jacob Metius of Alkmaar.

Fountains of Bryn Mawr (talk) 16:11, 7 December 2008 (UTC) ''


 * I am OK with that. Are we reaching a consensus of some kind? Martin Hogbin (talk) 20:45, 7 December 2008 (UTC)


 * I think it's important that we cite sources for whatever we say. It's unclear to me why Fountains thinks it's OK to add this stuff about Greek and Indian contributions without citing a source, when he has been complaining about the sourcing of mentioning Alhazen.  I also don't think we have to form a final conclusion here.  It is OK to continue to rework the details, as long as we move in the direction of a history summary this is increasingly well supported by sources.  It appears to me that Fountains is still over-reacting to the guy who was pushing the Islamic names, to the point where he seems intolerant of them; since many sources mention Alhazen and Ibn Sahl for their roles, I don't think it would hurt to mention them. Dicklyon (talk) 22:32, 7 December 2008 (UTC)


 * If we follow this path we get:

''The lens and the properties of refracting and reflecting light had been known since antiquity. Optical theory was developed by ancient Greek and Indian philosophers, expanded on in the medieval Islamic world, and had reached a significantly advanced state in early modern Europe. Concurrent with thoretical developement was the practicle developement of lens manufacture for spectacles, first in Venice and Florence in the thirteenth century , and later in the spectacle making centers in both the Netherlands and Germany. It is in the Netherlands in 1608 where the first recorded optical telescopes (refracting telescopes) appeared. The invention is credited to the spectacle makers Hans Lippershey and Zacharias Janssenin Middelburg, and the instrument-maker and optician Jacob Metius of Alkmaar.

''An Italian scientist greatly improved upon these designs the following year and is generally credited with being the first to use a telescope for astronomical purposes. His telescope used Hans Lippershey's design of a convex objective lens and a concave eye lens. A German schoolteacher proposed an improvement on the design that used a convex eyepiece.''

The theoretical advantages of the reflecting telescope, which uses a curved mirror in place of the objective lens, were known almost from the invention of the refracting telescope, but an Englishman has been generally credited with constructing the first practical example in 1669.


 * I could go on, but I hope you can see my point - it makes no sense to remove the names where they are known, and including some but excluding others seems a form of WP:UNDUE or synthesis. Also, the reference to  a significantly advanced state in early modern Europe seems counter-productive.  It's out of chronological order, (optics was improved in Europe after the first telescope)  and again implies that optics was a pre-requisite for the first telescope, a conclusion that at best is insecure.  And I still think it's best to lead with a statement that telescopes are based on lenses/mirrors and optics.  This ties together the discussion that follows, all of which is about one topic or the other.  LouScheffer (talk) 22:38, 7 December 2008 (UTC)


 * The reference to ancient Greek and Indian philosophers comes from the summery at the Lens (optics) (History of optics), one can only hope some reliable referencing went into that summery and the others I quoted --- but yes, it can be 100% bullshit, you have to check such things. Thats the problem I have been encountering with each and every article, you clean one up and the you find the relating articles are pure shit. Welcome to my world (maybe its simply the common world of Wikipedia). Since we are dealing with summaries here I would suggest relying on the other summaries for now, unless you are talking about scrapping Wikipedia its self and bringing every other editor out there into this discussion. Now the information at Lens (optics) seems right. "advanced state in early modern Europe" refers to the progression of optical theory through thinkers such as Euclid, Ptolemy, Ibn Sahl, Alhazen, Witelo, Roger Bacon, and Johannes Kepler. Keplers "Astronomiae Pars Optica" "the foundation of modern optics " was published in 1604 (four years before the invention of the telescope). Please check the other "history of the telescope" reference articles above and you will find references to the fact that Kepler theories are different from those of Ptolemy and Alhazen, reflecting a much more advanced thinking. As to "remov(ing) the names", we seem to have a total misunderstanding of Wikipedia's core content policies here. Wkipedia articles are made up from the general scholarly record and predominance of material in reliable sources and the accurate balanced citing of those sources. Its the difference between this and this. As to counter-productive history, welcome to the can of worms. The telescope does have that dual history, totally missed by the great optical thinkers (who had philosophical reasons for not even thinking of such a thing re: the Ptolemaic view of the universe), built by practical opticians, and then developed by the optical thinkers. You can cover this in a balanced fashion in a very long article like History of the telescope but being balanced in a summery is much harder. Fountains of Bryn Mawr (talk) 15:22, 8 December 2008 (UTC)


 * To "only hope" that another article is well sourced is not going to help move along in improving this one. Check the sources and cite them, as you are asking others to do, when you propose new wording, so that we can focus on the question of balance and detail instead of wondering what's behind your additions.  Many of the objections to mentioning Alhazen were based on the sources not being reliable, but that was apparently just a red herring, since many histories of the telescope do in fact talk about his contribution.  Dicklyon (talk) 16:53, 8 December 2008 (UTC)


 * Most of what is in that summary version is easily referenced. Greek contributions for example, are very prominent in the scholarly record and have reliable references cited on this very talk page, just scroll up. "Indian philosophers" is a bit more iffy. The problem with Alhazen all along has not been the sources not being reliable or that no sources talked about his contribution, its that the sources did not "directly support the information as it is presented in an article" nor were they "appropriate to the claims made" WP:SOURCES. There are simply way to many contributors to the history of optics for use to unduly cite just one in a "claim" that no plurality of reliable sources make. Fountains of Bryn Mawr (talk) 17:15, 9 December 2008 (UTC)


 * Having read the article on the 'History of the telescope' it would seem to me that mention of individuals who contributed to optics generally is not justified as no particular person made a particularly important contribution. I therefore now support something more along the lines of that suggested by Fountains of Bryn Mawr, where no names are mentioned before 1600. Martin Hogbin (talk) 22:36, 8 December 2008 (UTC)


 * I agree with Lou in regards to adding at least a couple sentences on the scientific conclusions made to light and lenses. InternetHero (talk) 00:59, 9 December 2008 (UTC)


 * I think we're all in agreement that we shouldn't mention anyone unless there are multiple reliable sources that discuss their contribution in relation to the telescope. Alhazen easily passes this test.  Who else are we arguing about? Dicklyon (talk) 18:09, 9 December 2008 (UTC)


 * I have to disagree with you there, he did no more towards the invention of the telescope than say, Euclid, Ptolemy, Ibn Sahl, A Witelo, Roger Bacon, and Johannes Kepler. None of these is really significant in that respect and I think it best to omit them all. Remember there is an article 'The invention of the telescope' which has all the detail.Martin Hogbin (talk) 18:32, 9 December 2008 (UTC)


 * I have no knowledge of, nor intention to argue about, who did how much. I thought we were going to use a more objective criterion, like the one I pointed out above.  Did you look at the books I linked earlier? Dicklyon (talk) 18:36, 9 December 2008 (UTC)


 * If there are reliable sources stating that Alhazen or anyone else played a major part in the invention of the telescope then I agree they should be named. What source states that Alhazen played a major role in the invention of the telescope? Martin Hogbin (talk) 19:24, 9 December 2008 (UTC)


 * Remember, this is history of the telescope, not history of the invention of the telescope. Alhazan invented the parabolic mirror, the heart of most astronomical telescopes (and this influence is quite direct).  He also was a primary source for the later opticians, such as Kepler, who also contributed to telescopes.  LouScheffer (talk) 20:31, 9 December 2008 (UTC)


 * Alhazan did not invent the parabolic mirror. Ibn Sahl wrote about parabolic mirrors and Alhazen did not cover conic sections in his work (at least according to that source). Kepler's work is such a radical departure from Alhazen it is hard to point to Alhazen's influences 600 years later. And we are talking about theoretical refinements that come after the invention of the telescope, there is allot of science and contributors that made them possible. Fountains of Bryn Mawr (talk) 21:21, 9 December 2008 (UTC)


 * Well Archimedes might (or might not) have been the inventor. Ibn-Sahl is the first unambiguous inventor (and discovered the correct law of refraction as well).  But the analysis of these mirrors of Alhazan is the one that's most relevant to the history of telescopes, since his work was translated, and hence available (and quoted by name in) the next generation of optical advances (Kepler, Snell, Descartes, Fermat).  This continues until today - just try to find a copy of Ibn-Sahl's treatise On Burning Mirrors and Lenses, whereas the Latin translation of Alhazan's text has ISBN 0384007309 and is  available from Amazon.  The sales rank is not so great (#4,432,413), but still impressive for a 1000 year old scientific text in Latin... LouScheffer (talk) 05:24, 10 December 2008 (UTC)


 * Although this may have little relevance to a summery of the history of the telescope, it good reference material for the history of the Parabolic reflector. Will add some there. Fountains of Bryn Mawr (talk) 18:41, 20 December 2008 (UTC)

Incidentally, when looking this stuff up, you need to keep in mind Alhazan's name was also spelled Haitham and Haytham and Alhacen and many other ways... LouScheffer (talk) 05:24, 10 December 2008 (UTC)


 * So when can we stop argueing about non-sense and add the information already? We have no consensus in respect to Al-Haytham being an inherent part of the telescope. InternetHero (talk) 19:55, 18 December 2008 (UTC)


 * Since there are at least three of us arguing for a small pre-telescope history paragraph, I added one, with badly supported info and dupication edited out of the one that InternetHero had. I'm not saying it's perfect, but it's better than saying nothing there. Dicklyon (talk) 17:10, 19 December 2008 (UTC)


 * "Saying nothing" is the prefered way to go by Wikipedia policy: "Passages open to interpretation should be precisely cited or avoided." (WP:OR-Using sources). Please note: consensus discussions are not votes. Additions such as this have to follow prevalence in reliable sources and the outside observer above (not brought in by me) sees problems with this version of history. Fountains of Bryn Mawr (talk) 18:28, 20 December 2008 (UTC)


 * I would suggest that a sentence or two might be added about the history of the telescope before 1600 but that no particular person is sufficiently prominent for them to be mentioned by name. Martin Hogbin (talk) 19:22, 20 December 2008 (UTC)


 * Histories of the telescope often do mention these names. Let's include them, since they're well sourced, and only add about a line to the summary.  Or please explain better what is the objection that makes you two keep taking out well-sourced stuff. Dicklyon (talk) 19:45, 20 December 2008 (UTC)


 * Just because something is well sourced does not mean it must go in this article. The problem is that there many people with some, well sourced, connection to the history of the telescope before 1600 but none of them stands out above the others for special inclusion.  We should therefore add them all, which in my opinion is excessive in one section of an article, or none, which seem to me to be the best solution in this case. Martin Hogbin (talk) 23:35, 20 December 2008 (UTC)


 * Who else do you have in mind? Dicklyon (talk) 02:29, 21 December 2008 (UTC)


 * A brief search through WP finds: Abbas Ibn Firnas, Nicholas of Cusa, Robert Grosseteste, John Dee, Thomas Digges, Euclid, Pappus, Hero of Alexandria, Claudius Ptolemy, Abu 'Abd Allah Muhammad ibn Ma'udh, Aristotle, Avicenna, Averroes, al-Kindi, Tideus, Constantine the African, John Pecham, and Witelo. Also worthy of mention a bit later are: Willebrord Snellius and René Descartes.


 * What is your justification for singling out the names that you have added? Martin Hogbin (talk) 10:44, 21 December 2008 (UTC)


 * Before we get into the details of whether the ones we mention are the best choice, we need some consensus that it's OK to have a brief paragraph on the prehistory, precursors, and relevant contributors to telescopes. After that, we should settle are names that are explicitly associated with the telescope in mulitiple reliable sources.  Some of your names probably fail on that; I had to do a bit of a search for the Abu guy, to find a place to link, and there's nothing there about him and telescopes, just general optics, so I'd leave him out.  The others I haven't reviewed yet, but would be willing to do so. Dicklyon (talk) 17:49, 21 December 2008 (UTC)


 * So far, I find no mention of telescope on any of the WP articles of any of those guys, whereas it is mentioned for all the guys I linked in the article (and no, it wasn't me who those mentions in). I realize that we can't use WP as the justification, but this suggests that maybe we're not far off from a reasonable selection.  If you'd like to consider alternatives, you'll have to provide some sources to suggest why those names are relevant.  Dicklyon (talk) 17:55, 21 December 2008 (UTC)


 * Personally, I would be happy to have a sentence or two on the subjects you suggest but I do not think any person made a significant enough contribution to be mentioned. Martin Hogbin (talk) 18:02, 21 December 2008 (UTC)


 * We hear you already. Dicklyon (talk) 18:17, 21 December 2008 (UTC)

(de-indent) This talk page is already repleate with sources on this topic. I have listed sources relevant to the history of the telescope below and have re-written the relevant sections based on them. Fountains of Bryn Mawr (talk) 16:18, 7 January 2009 (UTC)

(add sources here)
 * History of telescope sources:

Secondary sources
 * The History of the Telescope By Henry C. King
 * Stargazer by Fred Watson

Tertiary sources
 * galileo.rice.edu The Galileo Project
 * The First Telescopes

Secondary sources
 * History of lense sources
 * "Renaissance Vision from Spectacles to Telescopes" By Vincent Ilardi,

Secondary sources By Thomas Little Heath
 * History of mirror sources
 * An Acre of Glass By Jack B. Zirker
 * A History of Greek Mathematics : From Aristarchus to Diophantus.

Some big picture points
Here are some potentially missing points, in no particular order:
 * Reflecting telescopes were guided by theory, but the mirror technology is hard. Note that the optics used in the Hubble were understood in 1632, and the mirror mis-manufactured in the 1980s.  The Hale (Palomar) 5 meter was the last big parabolic mirror, since Hale thought the project risky enough already.  All big telescopes since then are Ritchey-Chrétien telescope or more sophisticated yet.
 * In comparison, theory did not help much with refractors, and in fact set them back. In particular, Newton thought an achromatic lens was impossible, and this discouraged research for many years.
 * On the other hand, Newton invented the pitch lap, the key to polishing reflectors for the next few hundred years.
 * In many cases there are three contributors, the person who first discovered it, the person who popularized it, and the person who made it work. Cavalieri (1632) and Mersenne (1636) invented the Cassegrain and Gregorian reflectors, Gregory (1663) and Cassegrain (1672) made them popular (all before Newton's reflector) but could not make them work, but later Hooke (1674, Gregorian) and (???, Cassegrain)  figured out how to make the mirrors and make them practical.
 * Many modern telescopes are optimized for etendue as well as diameter. For many research programs, field of view is as important as mirror size (since in a large angle investigation or survey, one can be traded for the other.)
 * Modern telescopes have no need to accomodate a human observer at the focus, though this was a requirement for many years.


 * Those look like important points that could be added to the article. Why not  give it a go, be bold.   Martin Hogbin (talk) 19:19, 20 December 2008 (UTC)

Corrections
I reworked the History section for prose style, focus, and to fit summary style and other guidelines. Also several misstatements of fact or mis-quotes of reference. Several referenced sections were a bit to detailed for a summary of telescope history but should be added to History of the telescope.

RM first statement since it is a statement of fact that is un-referenced WP:V, not invention of "science” by referenceFred Watson, Stargazer (page 55) . Removed single thinker examples “Archimedes”, “Alhazen” ect, references do not specifically say this WP:V, citing one person per each era is back to WP:UNDUE. Alhazen as first to put "Optics on a scientific footing" is a misreading of King and contradicted by ref . Powers as a source is unreliable as used since it should not be used for statements of fact WP:RELY.

Summery of introduction of achromatic lenses was missing. Statement “Theory was of little help in the development of refractors” is broad, redundant to intro and was a quote referring to Hyperbolic lenses, a bit off topic to the purpose of a summery. No reference as to how an Aspheric lenses is an important summery step in the history of telescopes so reworded. These should be added to HOTT if they can be put into historical context.

Reflecting telescopes were known almost from the refractors invention

Watson says Bonaventura Cavalieri had theories similar to Cassegrain and Gregorian, he did not intend them as telescopes, and they were not “known by 1632”, they were, in fact, known by 1975, and citation of Bonaventura Cavalieri is more of a footnote to history of telescopes than a summery “fact” (WP:RELIABLE). Should be added to HOTT if it can be put into historical context, if any.

James Short did not make the first parabolic mirrors, just perfected fabrication. Parabolic mirrors were being used in Gregorian telescopes being built by Robert Hooke in 1673

In a summery, Newton’s contribution would be a working reflector, not the pitch lap and source says he my not have invented it.

Schmidt Cassegrain is a commercial subgroup of the real invention, the Schmidt camera. Schmidt cameras were not invented so the corrector could to support the secondary, in fact they don’t in research telescopes, and dust seal was not a priority, they were invented for wide field work.

Fountains of Bryn Mawr (talk) 03:41, 18 January 2009 (UTC)

History of the telescope in magazine 'science' (cartoon version)
Science, of the AAAS, has produced a cartoon version of the history of the telescope. It's at A brief history of the telescope by Larry Gonick and William Alschuler. It makes many of the same points we do, although there is more on achromatic lenses and less on reflectors. The people mentioned at Alhazan, Lippershey, Janssen, Galileo, Kepler, Gregory, Newton (including his error about achromatic lenses), Hall, Bass, Dollond, Hershel, Rosse, Hale, Schmidt, (then segmented mirrors and adaptive optics with no names).

Although their has more humor (about ridiculously long refractors, and the folly of siting telescopes in Ireland) I think the version here (at least in some incarnations) has more info in the same or less space.

What does everyone else think?? LouScheffer (talk) 00:58, 19 January 2009 (UTC)


 * That article seems to be subscription only (at least I can't get to it:. FYI there is a whole series of videos on the topic at the Institute and Museum of the History of Science. They give a basic outline and bring up room for improvement (they show a second inventor for mirror silvering, ect) and other milestones. It may not pertain to this summary article, except for some changes in the footnotes, but it looks invaluable for History of the telescope. Fountains of Bryn Mawr (talk) 15:47, 21 January 2009 (UTC)


 * I tried this again. You are right, it's subscription.  I did not notice since at work we have an institutional subscription, automatic by IP address, I think.  I suspect most schools or research institutions will have this.   From home I needed to use my AAAS membership to see the article (if you are a AAAS member then you can get digital access at little or no charge..)   LouScheffer (talk) 13:46, 23 January 2009 (UTC)

Visible spectrum telescopes merger

 * Redirect to Optical telescope - Clearly a duplicate article. Some ref'ed material could be merged. Fountains of Bryn Mawr (talk) 16:01, 14 April 2009 (UTC)


 * It's not worth a discussion, as it's just a recent inadvertant content fork; just redirect it here and tell the author to put anything new here instead. Dicklyon (talk) 02:12, 15 April 2009 (UTC)

Pay telescope should be removed because it is not referenced and even binicular section does not include a pay binocular. Pay binicular would be much more common. —Preceding unsigned comment added by 68.150.139.173 (talk) 03:53, 28 April 2009 (UTC)
 * Merge/redirect.--Srleffler (talk) 01:44, 15 May 2010 (UTC)

Optical Telescope Critique
The invention of the telescope can be seen as the first door that was opened to more information about Space. In the Wikipedia article, “Optical Telescopes,” the writers go into the specific history of the optical telescope. The history section has a plethora of information regarding the telescope. One of the most striking comments within the article was on the first line, which states, “The telescope is more a discovery of optical craftsmen than an invention of scientist.” This comment was well stated, because it shows that technological development does not have to come from those within the specific field of study of the technology. For example, the optical telescope, according to Wikipedia, was credited to a pair of spectacle makers. In addition, the writing talks about who the inventors of the telescopes where and even around the time period that the telescope was invented. Moreover, the piece referred to the additional people that improved upon the design of the telescope, like Galileo and Johannes Keppler. The article goes on to describe how the optical telescope was the gateway to other telescopes, like the refracting telescope. The last part of the writing refers to how the optical telescope led to the development of other telescopes, like the refracting telescope.

While the article was easy to read, there were a few issues with the grammar and format of the piece. One such instance of a grammatical error was within the first paragraph of the history section. It reads, “The lens and the properties of refracting and reflecting light had been known since antiquity and theory on how they worked were developed by ancient Greek philosophers, preserved and expanded on in the medieval Islamic world, and had reached a significantly advanced state by the time the telescope’s invention in early modern Europe.” The sentence is long-winded and wordy. In addition, the sentence does not flow and has some grammatical issues. Instead of saying “and theory on how they worked were developed,” the sentence should read, “and the theory on how it worked was developed.” This is not only grammatically correct, but it also helps the sentence flow. Furthermore, about half of the article refers to how the optical telescope aided in the development of other types of telescopes. In my opinion, the article should have spent more time talking about the invention than the overall impact of the telescope. It makes the section shift from a historical section to an impact or result section.

Overall, the history section has absolutely no pictures in the historical section of the article. Instead of having no pictures, the article could have placed pictures of the historical figures that helped aid in the invention or advancement of the technology. For instance, a picture of Galileo could be used, because he was the first to use telescope for astronomical reasons. Another picture that would be useful within the writing would be a picture of an older model of the telescope. This could help viewers picture what the telescope originally looked at. Besides pictures, the article could also use more dates. There are only a few select dates and some are broad like the 13th century. Finally, the historical section alone has 19 citations. Most of these citations are from websites, like the “Galileo Project” And “MadeHow.com.” There are a few good secondary sources, like books, but some of the sources are dated as far back as 1975. If more information could be found on the telescope in current secondary sources, instead of websites and outdated writings, then the historical section would be more credible as a source of information.

When comparing the Wikipedia article about optical telescopes to the Encyclopedia Britannica article, within the first sentence there were discrepancies between the two. Britannica gives the credit to Galileo as building and using the first telescope for astronomical use, but does not mention the two spectacle makers from the Wikipedia article. The article is also more specific with dates and has the measurements of various telescopes. Furthermore, the article goes into more detail about what the telescope was able to see, like some of the planets. Similarly to the Wikipedia article, Britannica does not have any pictures within the section, but one the left hand side of the website, there is a photo galaxy with several images of telescopes. — Preceding unsigned comment added by HIST406-11rcaouett (talk • contribs) 03:29, 5 October 2011 (UTC)

Famous optical telescopes?
I removed the list "Famous optical telescopes" per WP:LIST (can be seen here) because the list's inclusion criteria is undefined - all optical telescopes listed in Wikipedia are "Famous" (notable) - to pick some as more famous seems to be against WP:NPOV. There may be a way to re-include the list with a non-POV definition/inclusion criteria so editors won't be guessing what should be in the list, but I don't see one. The list may simply be redundant/unnecessary since "See also" section already has links to all definable lists. Fountains of Bryn Mawr (talk) 19:19, 26 June 2012 (UTC)

How big can they get?
I have just finished reading the last part, about the limits, and found it very interesting, well-written, and informative. However, I was disappointed not to find the answer to the question that caused me to read it in the first place: what are the limits to a space-based optical telescope? Could one be built, in theory, big enough to read a newspaper headline on the moon, for example? How about on Pluto? It seems to me that you'd reach a point that you'd run into trouble because of how many photons there can be per square inch, or some such thing, some kind of law of physics that limits how strong an optical telescope can be before you'd run into problems of the limits of photons to be magnified indefinitely. Chrisrus (talk) 07:27, 10 February 2013 (UTC)
 * I would say there is no limit on size for a space-based telescope. Obviously, a 100AU diameter mirror won't be orbiting the Earth, but such could be built in intergalactic space somewhere.  The usefulness of such an instrument would be limited if it takes a million years to transmit the images home.  I remember talk about building an inframeter with a base line of 5 or 10 AU's, but you asked about optical telescopes.  I don't think there's so much a "law of Physics" that limits magnification, except that your eyepiece may get hot enough to melt, but you'd be blinded by then.  The major limit would be space debris, as just one 100 foot astroid would wreak a gazillion dollars of equipment.  I'll stick my neck out here and say Hubble could read a newspaper on the moon, if Hubble had the right sensing equipment on-board, and the headlines were the size of a football field.
 * I've polished out 6 inch mirrors, the 10 m Keck is just insane in my opinion. - Watchwolf49z (talk) 01:30, 12 February 2013 (UTC)
 * Apart from the technical challenges of building large telescopes, aspects such as photon starvation may come into play. There is only a certain amount of photons emitted by a given source, and the size of the telescope cannot change that. --Nicalacla (talk) 12:31, 12 February 2013 (UTC)
 * Thank you, Nicalacla. Please do add this fact about photon starvation and how it limits the theoretical power of optical telescopes.  Chrisrus (talk) 15:54, 15 February 2013 (UTC)
 * Photon starvation isn't really an issue for any realistic source. More area -> more photons detected, as long as the telescope itself subtends a small angle as seen from the source - in astronomy, this will always be true (not in e.g. microscopy). Actually, the main limitation for the size of a space telescope is the size of the payload fairing on the rocket that lifts it into orbit. Mirrors bigger than about 3.5m (the size of the Herschel mirror) simply won't fit on any current rocket design. JWST gets around this with a segmented mirror which deploys in space, but the technical challenges in that design are immense, and we still don't know if it will work. Modest Genius talk 14:55, 14 September 2013 (UTC)

Amalgamation of properties
I'm considering putting a few characteristics under a single heading with the characteristics as sub-headings (also expanding more specific information), these properties include; Is anyone against a cleaner layout and more informative specific optical telescope properties? Dr.  Smash  14:29, 9 December 2013 (UTC)
 * Focal length and f-ratio
 * Light-gathering power
 * Magnification
 * True FOV vs. apparent FOV


 * Looks good. I was noticing for a while that this article seems to be missing "Magnification", the first thing a reader would probably want to know. FOV was a good add as well. The section "Focal length and f-ratio" should probably be "Focal length and focal ratio" since focal ratio is the correct term and Wikipedia asks that full words be used before abreviations. Fountains of Bryn Mawr (talk) 17:23, 9 December 2013 (UTC)


 * I have sent a request to Starizona, a source for a large part of the magnification information, for the permission to use their images. These are great examples of diffraction and image quality which I really think the topic deserves and provides the most accurate display of factors which I could find on a short basis. Dr.   Smash  03:55, 10 December 2013 (UTC)


 * I may have gone a bit overboard with specific information and really require some input on the vastness of information which could be included and what not to. The information can easily be placed elsewhere however it directly relates to the optical performance and capabilities of optical telescopes, the wiki pages where it could be placed don't originally contain the information. The topics in question refer to the characteristics; further information on minimum, maximum, optimum and wide-field magnification with more specific formula (they are only standardized at the moment), eyepiece focal length and formulas relating with how it affects the other characteristics and viewing capabilities, determining maximum performance from the telescope using the correct accessories, more information on exit pupil relations, magnitude limits and expansion in light gathering power. More information can be found at rocketmime.com/astronomy. I would imagine the first stop for someone wanting information would be directly to the telescope page, rather than ciphering through various articles on viewing performance, this is where the usefulness comes in. I will add some info into my sandbox while hopefully we can make an informed decision about what information can be included. Dr.   Smash  08:19, 10 December 2013 (UTC)

Formulae citation
A quick note of the reference equations used in many of my content additions, I tried to cite the equations without using the same values used in them. Such values are based on approximations, eg. Moon values are referenced from the Wikipedia Moon characteristics rather the supplied values on the reference page. In some cases a mean value was used in place of an approximation, such as Earth-Moon distance or angular diameter. This gives a more precise syntax where a user can directly reference values from within Wikipedia to achieve the same results. The overall effect just means that some of the values don't match cited references, however the equations do. Dr.  Smash  02:23, 18 December 2013 (UTC)

Lenses and Filters
Dark glass is not safe enough, see Arc welding lenses, see Telescope solar lenses.

was added as correction

Please either say nothing, refer to manufacturer instructions, or correctly say it is a special solar lense. Dark glass alone will cause blindness over time.

This is also true for cheap* sunglasses but don't tell anyone!

(Cheap sunglasses use dark material and the eye feels safe but is actually being damaged at wavelengths that do not cause pain. A doctor would suggest squinting eye lids instead of relying on cheap sunglasses for eye pain situations)

Never look at arc welding using dark sunglasses. — Preceding unsigned comment added by 72.219.202.186 (talk) 14:51, 9 April 2014 (UTC)

Schematic of a Keplerian refracting telescope
Isn't this diagram utterly useless? It completely lacks clear labelling,and for the life of me,I can't figure out what difference between the red and black lines are.

Perhaps it should be clearly labelled,so the people who lack knowledge about telescopes(i.e,your target audience) should be able to gain knowledge about telescopes. As it is now,I think it is quite useless.182.181.152.111 (talk) 06:33, 28 April 2014 (UTC)

Inverted, everted
I found no evidence in the OED, in Wiktionary, or elsewhere that either "everted" or "reverted" means "reversed left to right". Maybe I read the entries too hurriedly. Is there another source?

It confusing to say that "telescope designs produce an inverted image" and at the same time "the image is both inverted and reverted". This gives "inverted" two incompatible meanings, one of which is defined as the other plus something else. While it could be argued from dictionary entries that "inverted" could mean either of these, the reader should leave with only one meaning for this technical term in the telescope context. 129.132.209.199 (talk) 23:42, 7 June 2014 (UTC)

Afocal system
Should it be mentioned somewhere that optical telescopes are afocal systems? Shmayo (talk) 13:29, 12 March 2015 (UTC)

"Directly proportional"
Hi folks. As an astronomy professor, I thank you all for your contributions to making this article better. I made a change in the introduction, to clearly state the proportionality between a telescopes aperture and its light gathering power and its resolving power. Resolving power, as previously stated in the article is "directly proportional" to aperture, in the mathematical sense:

https://en.wikipedia.org/wiki/Proportionality_(mathematics)#Direct_proportionality

Light gather power of course is proportional to a telescope's area, and thus to at the size of its aperture *squared*, as state later in the article.

Substar (talk) 17:25, 20 September 2019 (UTC)Substar