Talk:Reflecting telescope

Question on content for Celestron

Where did the above information come from? Celestron is a company that makes telescopes, particularly schmidt-cassegrains. Perhaps this Celestron was something sold in other countries? I've just never heard of this telescope design and would be interested in seeing some documentation.

I moved User:172.158.63.83's question above from the article space Maksutov paragraph to Talk here, and it's a good question; it sounds a lot like the Questar [1] as that was a Maksutov but I cannot get detailed specs of how the finder and main mirror were integrated. However Celestron also make a Maksutov design with a flip mirror, so I'm not sure. -Wikibob | Talk 12:10, 2004 May 20 (UTC)

I looked up Questar telescopes and found on Company 7's page a description [2] that matches. I also looked up the Questar site [3]. On Celestron's site I found [4]. Basically, the paragraph in question could probably be clarified.... Elizabeth (User:172.158.63.83)kljuhugtft=ftrey

I modified the Maksukov reference to Questar... the flip mirror (it was really a sliding prism)/"viewfinder" is covered in Questar's early 1950's patent, and was (and still is) a hallmark of the scope. At $1000 (1957) then and today's $4000 (for a 90mm diameter scope), it has forever been in the "luxury" class. ... Dick (User:128.95.100.19)

I removed the section describing the Questar's built in finderscope - This article seems to specifically describe optical designs, not commercial brands. The Questar is not a separate design type and the Questar's addition of a built in finder has nothing to do with the Maksutov design.Halfblue 12:30, 17 September 2006 (UTC)

I disagree. The questar design is another unique implementation, particularly the finder mechanism. Garglebutt / (talk) 23:07, 19 September 2006 (UTC)

The page seems to be about unique optical designs and their variations. The section in question is about the Maksutov design. Questar's mechanical design of having the finder co-use the eyepiece with the main OTA is, as you say, a "mechanism", not a modification of the Maksutov optical design -- so it should not be listed as a Maksutov variation.Halfblue 03:48, 20 September 2006 (UTC)

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how does a spherical mirror have less magnification than a parabolic mirror of the same focal length? Rsduhamel 03:21, 31 Dec 2004 (UTC)

it doesn't. Duk 08:53, 31 Dec 2004 (UTC)

Oops, my mistake. Must have had too many tabs open. I meant to post this question on the talk page for Schmidt corrector plate. Anyway, Duk, you know that, and I know that but the page on the Schmidt corrector said different. I have made the correction. Rsduhamel 06:40, 1 Jan 2005 (UTC)

Newton or Hooke?

I believe that it is important to note that there is debate about whether Isaac Newton or Robert Hooke (http://en.wikipedia.org/wiki/Robert_Hooke) invented the reflecting telescope. There appears to be no debate that Robert Hooke first demonstrated it, which should be noted in the reflecting telescope page.

Speisert 07:16, 8 December 2005 (UTC)

Yes that should be added, if there is an authoritative article you can reference maybe there should be an opening sentence along the line of "There is some debate as to the origins of the reflecting telescope [5]". I have been cleaning up the recent adds coming in and moved it all into a "History" category. Those adds have no citations and if you take them at face value it states that Hook built the Gregorian design in 1673. That would mean that Newton built the first practical model in 1670. That section should probably be expanded to explain the limitations of early speculum metal and silver coatings that limited reflector design. 69.72.93.219 15:06, 16 December 2006 (UTC)

Changes to "Cassegrain focus" and "Maksutov-Cassegrain" sections

I am moving the section on Vixen telescope models to this talk page. They need to be rewriten to describe a specific optical design, (i.e. name/type of design), not a comercial model:

Vixen produces an 8 inch aperture modified Cassegrain design they refer to as a VISAC (Vixen Sixth-Order Aspheric Cassegrain). It has a fixed primary mirror with an open tube rather than a corrector plate and provides correction of aberrations via lenses in the draw tube of the focusser. The design has no coma and exceeds Ritchey-Chrétien performance by also addressing field curvature while being cheaper to produce. This particular design is also unusual in that it is a Cassegrain design but has a refractor style rack and pinion focuser.

Vixen produce 8, 10.25 and 13 inch aperture modified Maksutov-Cassegrain design. It has an open tube rather than a corrector plate and provides correction of aberrations via a two element miniscus corrector lens in front of the secondary. This design was originally envisaged by G. I. Popov with a practical implementation by Yu. A. Klevtsov. The 8 inch employs a refractor style rack and pinion focuser while the larger apertures move the primary mirror as in most other Cassegrain designs.

Halfblue 01:24, 17 September 2006 (UTC)

This is a specific optical design which only one manufacturer produces and has a number of unusual aspects. How do you envisage it being incorporated as I see nothing particularly wrong with the section you have removed? Garglebutt / (talk) 23:04, 19 September 2006 (UTC)

The article is about designs - not commercial models, although the article does tend to wander off topic---- something to be addressed in a future cleanup. Both sections above set off my "spam detector" since they start with a commercial company's name and then make claims about their products specifically that are not backed up by citations (such as "exceeds Ritchey-Chrétien performance" and "cheaper to produce"). Many commercial and non-commercial designs have "unusual aspects" such as a corrector lenses somewhere in the OTA and cassegrains with rack and pinion focusers so why are these designs by one company being highlighted??? That is very fishy. If the design its self is unique and needs to be noted then that design should be described by its generic optical design/name/inventor and maybe at the end of the paragraph it could be noted that "company XXXXX is the only known commercial manufacturer of this design".Halfblue 04:19, 20 September 2006 (UTC)

I seem to be missing a point here. There is no prescriptive detail on what this article should contain and if it were only about designs then a lot of the current content and images should be removed. I added the original Vixen content because I considered the designs to be sufficiently different from standard designs to warrant a mention.

The modified Cassegrain VISAC appears to be a Vixen created design (although it probably borrows from their modified Maksutov-Cassegrain). The modified Maksutov-Cassegrain does provide information on the creator and how it differs from the traditional Maksutov-Cassegrain so this seems ok. Implementation of designs is relevant and encyclopedic and in both cases providing details on how features have been implemented adds value to this article.

Rack and pinion focussers on Cassegrain telescope are very uncommon and I suspect Vixen are the only company to provide this with correctors in the draw tube, which I also consider relevant information. Vixen's telescopes are much cheaper than Ritchey-Chrétien telescopes. This is easily confirmed by picking up any astronomy magazine or looking at an online store. Ritchey-Chrétien telescopes tout the superiority of their design based on a number of standard limitations with optics. The VISAC has the same optical correction as a Ritchey-Chrétien as well as correcting field curvature so although probably a little commercial sounding, performance comments are also true. Garglebutt / (talk) 04:47, 20 September 2006 (UTC)

Do Catadioptrics belong here?

It seems to me that the Catadioptric type telescopes (Schmidt-Cassegrain, Schmidt camera, Maksutov-Cassegrain) should be moved to their own section header "Catadioptrics" in this article since they are similar mirror/lens designs. Maybe they should be moved to their own article since they are Catadioptric telescopes, not Reflecting telescopes (the two designs are usually described as being distinctly different "types") . Halfblue 02:14, 17 September 2006 (UTC)

There are main articles for quite a few of the reflecting types. I don't see any particular value in having another article while this article is not overly long. The Vixen VISAC is a good example of a hybrid design that could fit in either camp. Garglebutt / (talk) 23:10, 19 September 2006 (UTC)

The opening paragraph of this article describes "Reflectors" in such a way as to exclude "Catadioptrics" -- i.e. "an optical telescope which uses a combination of curved and plane (flat) mirrors to reflect light and form an image, rather than lenses to refract or bend light to form an image.". So we have a contradiction within this article since Catadioptrics do use lenses. The Vixen products you are noting are Catadioptrics… its just that their correction elements are not “corrector plates” in the front of the system. I have always seen three categories of telescopes listed ---> Refractors, Reflectors, and Catadioptrics. It makes logical sense we should have three articles covering those 3 types and that one type should not be listed on the other's page.

A bigger problem may be that this article its self should not exist. As you noted "There are main articles" for what’s in here. This thing really reads as a disambiguation page gone amok... maybe it should be trimmed back to just being that (a disambiguation page).Halfblue 04:42, 20 September 2006 (UTC)

I won't go as far as to remove this article but you are correct about some content misalignment. I'll move some of the content to the relevant articles. Garglebutt / (talk) 04:56, 20 September 2006 (UTC)

Moved a bunch of stuff out. I hadn't looked the whole group of related articles and I must admit there is quite a bit of redundancy. I'll add it to my list of ongoing refinements to be made. Garglebutt / (talk) 05:27, 20 September 2006 (UTC)

ok-- I shouldn't go to sleep here in the USA. Wow you moved alot! I wasn't expecting imediate action but Wikipedia does say "be bold". I was thinking "what constitues a "reflector telescope" and what does someone need to know about it when they come to this article?". Your right in that this article needs to stay since there is a "thing" out there call "a reflecting telescope" and Wikipedia describes things, and classes. I am going to make a few mods on that line.

ok done. I think the information on Maks abd Schmidts could be moved to the catadioptrics and arranged in a semi-disambigulation style similar to this page. I propose that and may do it soon unless there is some encyclopedic reason not to. Halfblue 13:39, 20 September 2006 (UTC)

More mods

Is a Dall-Kirkham a sub-variant of Cassegrain? Should it be moved up to be under Cassegrain?. I have a few pictures of "reflecting telescopes" that may work for a header picture in case the Ritchey 24" is too obscure. Halfblue 13:50, 20 September 2006 (UTC)

Found the info that points to Dall-Kirkhams being Cassigrains. I removed the information about Celestron and Takahashi based on them being non-encyclopedic since they are commercial references on a page that is not about commercial models, its about basic optical designs. They need to be on a page or section about commerial types, although I see no problem with those sections being linked back to their respective sections on this page under "See also". Halfblue 05:32, 21 September 2006 (UTC)

For now I've readded this as there is no dall-kirkham article and I believe it is valid to reference novel implementations of designs and it appears to be in context for the article to me. Garglebutt / (talk) 06:29, 21 September 2006 (UTC)

I have removed it again because the linked article astrograph states the Celestron f/6.8 astrograph does not exist and in fact Celestron has removed all info on it from their website. This is not the page to add information on commercially produced telescopes. This is a page on basic design. Wikipedia is not an indiscriminate collection of information WP:NOT. Wikipedia is an encyclopedia and edits should fit in an encyclopedic fashion. Commercial information should be added to their respective company pages or in a section in an article about commercial implementations of designs. I have also reverted edits by 165.138.178.3 since they were borderline vandalism. Halfblue 23:02, 21 September 2006 (UTC)

Hmm! That is interesting. I don't agree with your view of what is valid content however the fact that this example no longer exists makes the point moot. I should also point out that neither of the oft quoted WP policy pages has anything to do with providing practical examples of theoretical concepts. Garglebutt / (talk) 23:15, 21 September 2006 (UTC)

This has been responded at User talk:Garglebutt#Your edits re: Reflecting Telescope and Cassigrain since it goes a little more wide ranging than just this article. Halfblue 00:04, 22 September 2006 (UTC)

And I've responded on your talk page. Garglebutt / (talk) 22:10, 22 September 2006 (UTC)

Gregorian notability

Nevertheless, the Gregorian design was used most commonly in practice for the next century and a half. Cassegrain designs then became more popular.

I rv-ed this edit because it does not make much sense in context. Gregorian design was used most commonly? For what propose? As compared to what? By who? Is there a citation to support this? What exactly are you trying to say here? Cassegrain designs then became more popular. More popular than what? Please clarify this statement and maybe add a citation before re-adding it. 69.72.7.161 01:59, 15 December 2006 (UTC)

Eyepeice

Could someone please explain "eyepiece"? Does an eyepece have to have lenses in it, and if so, what lenses and why?

Also - it's prety obvious that a system that throws an image onto a photographic plate or CCD isn't one yuo can look through - you can't just put your eye at the focal point. So what's the deal there?

Hmmm... it did need a link to the article Eyepiece... fixed. That should contain answers to your questions. In general an eyepiece is a lens (more normaly a set of lenses) that magnifies the focal plane image and allows you to view it. 69.72.7.163 05:26, 2 February 2007 (UTC)

HERSCHELIAN

Perhaps the article should include mention of the Herscelian design, as a matter of historical curiosity. robert2957 12:21, 7 March 2007 (UTC)

Added section. Fountains of Bryn Mawr (talk) 15:17, 23 February 2008 (UTC)

Wooj telescope?

Moving below un-cited addition to talk. No ref to support this. 69.72.7.146 (talk) 01:31, 19 January 2008 (UTC)

===Wooj Focus===

Relatively new and currently used only in South Korea. This type of non-traditional reflector telescope uses prisms to focus wave lengths 430-27 nm. It is considered impractical because of high diffraction rates at certain latitudes. A Wooj telescope with 60" long prisms is set to be installed at the Seoul Observatory in March, 2008.

First to walk the length of the earth??

I call shenanigans on the suggestion that Newton was the first man to walk the length of the earth (whatever its 'length' means). Surely there were soldiers or couriers at the time who would have walked more distance than a scientist. Either that, or Chuck Norris was the first...

abu yousaf is proper gay —Preceding unsigned comment added by 217.155.49.4 (talk) 10:48, 14 January 2009 (UTC)

I fail to see the reference...

However, the phrase "Walk the Length of the Earth" seems to relate to a Buddhist paradigm. If a barefoot man was asked to walk the length of the earth on thorns, what should he do, cover the earth with leather, or cover his own feet with leather shoes?

So perhaps the analogy is that the Aristotelian view of the stars and the universe recreated the laws of nature to match the human ideals. Whereas, the Newtonian view (with Copernicus, Galileo, and others) was to give us the tools to understand nature as it exists in the universe. --Keelec (talk) 10:36, 5 August 2010 (UTC)

Off Axis Newtonian

There is a lot of info about Off Axis Newtonian Telescopes. Essentially using a parabolic lens, shifted. Often cut from a larger parabolic "parent" lens. As far as I can tell, visual defects are limited to those inherited from the parent lens. The focal length would be identical as that of the parent lens, but for a smaller lens and thus may appear to have unusually long focal lengths for the actual size of lens. Or if short focal length parent lenses are chosen, they often carry with them errors caused by the short focal length design. DGM is one small manufacture of Off Axis Telescopes. http://users.erols.com/dgmoptics/indexwelcome The individual segments of many larger segmented Newtonian telescopes, for example the James Webb Space Telescope, are essentially equivalent to off axis Newtonian Telescope Mirrors. --Keelec (talk) 09:06, 4 August 2010 (UTC)

Gregorian Telescope ray diagram

The lower green line on the left is incorrect. It should be parallel to the upper green line on the left since these rays are coming from infinity. It should be lower than the mauve line. The result will be that the angles of incidence and reflection at the primary mirror are equal for both the green line and the mauve line. The only way for that to be true at the moment is for the two rays to have different normals at the mirror. - Peter — Preceding unsigned comment added by 203.97.236.166 (talk) 22:22, 10 August 2015 (UTC)

Chromatic aberration.

The use of mirrors avoids chromatic aberration but they produce other types of aberrations.

Forgive my noobity on the subject; but given that lenses are ground from a cylinder on one side wouldn't they fundamentally be forming a achromatic doublet, or achromatic lens? So wouldn't they be intrinsically by design incapable of causing chromatic aberration? For example: https://en.wikipedia.org/wiki/Achromatic_lens BaSH PR0MPT (talk) 18:46, 19 October 2015 (UTC)

Sorry, don't follow. The linked article shows single element lenses are not achromatic (because they are fundamentally prisms, they make rainbows). Achromatic doublets are combinations of two pieces of glass, not a single chunk out of a cylinder, and they bring some colors together but are also not 100% achromatic. Fountains of Bryn Mawr (talk) 19:28, 19 October 2015 (UTC)

Gregorian incorrect

The diagram of light rays in the Gregorian Telescope cannot be correct. Someone has switched the green and purple segments in part of it. — Preceding unsigned comment added by 23.119.204.117 (talk) 05:19, 19 February 2016 (UTC)

Ritchey-Chretien Telescope

This telescope type is classified as Catadioptrics type of telescope in some sources and sell as a catadioptric telescope )( Gerçekler (talk) 04:37, 16 November 2021 (UTC))

Advertisements are not reliable sources, for obvious reasons. Fountains of Bryn Mawr (talk) 18:29, 16 November 2021 (UTC)

References

Multi-reflecting telescopes

This addition has no secondary sourcing to establish notability or even describe what it is. Patents and scientific papers are primary sources (see WP:PST) so need extensive secondary source coverage. This material also does not belong in an overview of Reflecting telescopes, there are a multitude of catadioptric lenses out there. Fountains of Bryn Mawr (talk) 11:39, 25 June 2022 (UTC)