Talk:Ritchey–Chrétien telescope

Amateur Use

I think the following statement should be removed:

"The RCT offers good off-axis optical performance, but amateur-size examples are relatively rare due to the difficulty of mass-production of hyperbolic primary mirrors. The Ritchey–Chrétien configuration is most commonly found on high-performance professional telescopes."

This is no longer true as many different manufacturers offer RCTs in the range of 6" to 14" aperture in price ranges of sub-$1000 for 6" models and only a few thousand for larger versions. As for sources, any quick vendor search shows this to be true and the original claim is not sourced.

Meade RCX/ACF

Should the Meade RCX400 be in here? The Meades aren't really technically RC's; they are more like a special variant of the Schmidt design. Meade is definitely taking some poetic license with the with term "Ritchey-Chretien" since they lack a hyperbolic primary. --unsigned by 24.6.109.20 at 06:06, 22 September 2005

The Meade reference was clearly a pathetic attempt to advertise their modified schmidt cass. The reference has been deleted. --unsigned by 69.177.110.144 (talk) at 05:26, 29 January 2006

Apparently someone reinserted Meade in the page again... Well, I'm attempting a cleanup while maintaining the reference. Please comment here before removing or adding further detail. Rnbc (talk) 18:50, 31 January 2008 (UTC)

As of 2/27/2008, Meade still lists their "Advanced Ritchey-Chretien" on their products page, using the RC designation in the model numbers ("RCX###"). It seems that they have created a new type of optics which they term "Advanced Ritchey-Chretien" which have many of the advantages of (as well as, according to Meade, advantages over) traditional/true RC optics. So, while Meade may have been successfully sued to force the change, it seems that they have been able to continue invoking the RC label through various "clarifications". I did not add this info to the main article as I am basing this entirely off a (admittedly brief) dissection of Meade's documentation. Chabuhi (talk) 21:37, 27 February 2008 (UTC)

Well, never mind me. Seems Meade has finally updated their online materials and is now calling their scope the ACF (Advanced Coma-Free). Though I note that they still invoke the RC label throughout. Chabuhi (talk) 14:04, 25 March 2008 (UTC)

Personally I don't see any reason why Meade should be given any column inches anywhere in the body of this article. I'd limit the Meade related information and the lawsuit to links and a small footnote. As has been shown they were never selling RC scopes so I don't think this article should be tainted by that sad episode. What do you think? BTW - I was the one that initially removed the blatant Meade advertising. --unsigned by 65.223.234.100 (talk) at 11:52/53, 4 September 2008

I'm removing the entire section and the reference to the lawsuit to the talk page. Doing so is better than tagging the article as WP:POV.Trilobitealive (talk) 01:29, 23 June 2009 (UTC)

==Meade Advanced Coma-Free== [[Meade Instruments]], of Irvine, California, introduced the RCX400 series of instruments in 2005, with mirror diameters of 10", 12" , 14" and 16", which they originally claimed were Modified "Advanced Ritchey-Chretien" Cassegrains. But in fact they were a version of a Schmidt-Cassegrain that delivers some advantages of the Ritchey-Chrétien design, such as a coma-free field, without all the associated cost. They were soon sued by makers of true Ritchey-Chretien telescopes because their "Advanced RC" design is actually a variation of SCT designs, and not directly related to the Ritchey-Chretien design. In January 2008, Meade settled the claim and agreed to quit using the initials RC in the name. By March 2008, model designations for the RCX400 had been changed to "LX400ACF", for "Advanced Coma-Free". This line of scopes was later "suspended indefinitely", due to bugs in electro-mechanical components, but the ACF optics are now used in their LX200 and LX90 scopes (now known as LX200ACF and LX90ACF). Removed section.Trilobitealive (talk) 01:32, 23 June 2009 (UTC)

Removed commercial link * http://www.star-instruments.com/lawsuit.htmlTrilobitealive (talk) 01:36, 23 June 2009 (UTC)

The material I've removed does not belong in this article. Interested persons might wish to add it to an article about the lawsuit.Trilobitealive (talk) 01:35, 23 June 2009 (UTC)

Schwarzschild deformation coefficient

Could 'Schwarzschild deformation coefficient' be explained in more detail? Now Schwarzschild links to a fairly useless page (black holes etc). —Preceding unsigned comment added by 128.214.3.229 (talk) 16:24, 6 November 2008 (UTC)

I looked at the source (Modern Optical Engineering), and not only does this term not appear there, it appears to be completely bogus. Not to mention that C1 and C2 are in fact just curvatures, and the equations presented are applicable to any two-mirror system and aren't specific to RCTs. 76.226.103.91 (talk) 08:51, 17 August 2009 (UTC)

Ok, the person who wrote 'Schwarzschild deformation coefficient' probably meant 'Schwarzschild constant', which is a synonym for conic constant. (The quantities referred to were curvatures, however, not conic constants.) Anyway, I cleaned up that section, because it was garbled and incomplete. 76.226.103.91 (talk) 07:31, 20 August 2009 (UTC)

Mirror Design Formulae

The formulas on this page do not specify the diameter of the primary and secondary mirrors. These formulas would be a useful addition in order to be able to design a RC-scope. —Preceding unsigned comment added by 128.214.3.229 (talk) 10:06, 21 August 2009 (UTC)

I guess the diameter is completely independent from this kind of calculation. There are more elements to making a sucessful complete instrument: choosing fitting mirror diameters, mirror support structure design, baffle placement, rigidity of the tube assembly, etc., all of which need their own separate calculations. --BjKa (talk) 13:11, 23 November 2016 (UTC)

Parabolic obsolete?

"the Hale telescope turned out to be the last world-leading telescope to have a parabolic primary mirror." I do not think this is true, many large observatory telescopes use paraboloids including most (maybe all?) that come out of the Steward Mirror Lab in Arizona. source: http://mirrorlab.as.arizona.edu/MISC.php?navi=FAQ) —Preceding unsigned comment added by 63.246.53.159 (talk) 07:45, 24 November 2010 (UTC)

That may be, but are they really "world-leading"? --BjKa (talk) 10:25, 23 November 2016 (UTC)

Nope. Basically no modern large observatory uses parabolic mirrors. The current generation (>1980s) are of Ritchey-Chrétien type with hyperbolic primary mirrors. The next generation will use TMAs. Steward Observatory is indeed world-leading in their mirror manufacturing, however, they prefer Gregorian-style designs like the 8.4m mirrors for the Large Binocular Telescope or the Giant Magellan--2001:16B8:118E:E200:232C:8D80:D9DE:CC65 (talk) 02:11, 20 December 2020 (UTC)

Ritchey's 24" for Yerkes

The 24-inch on display at Chabot (now returned to the Smithsonian) is a Newtonian built in the 1890s by Ritchey for the Yerkes Observatory, not an RC. There is some evidence that it had a broken Cassegrain configuration, but this needs to be verified. 69.143.209.231 (talk) 20:17, 15 May 2011 (UTC) DHD

e.g. ?

"Ritchey constructed the first successful RCT, which had a diameter aperture of 60 cm (24 in) in 1927 (e.g. Ritchey 24-inch reflector)." Should that perhaps be "(a.k.a. Ritchey 24-inch reflector)"? Fry-kun (talk) 21:25, 9 September 2011 (UTC)

Two-mirror foundation

It says: "If the mirror is made parabolic, to correct the spherical aberration, then it still suffers from coma and astigmatism, since there are no additional design parameters one can vary to eliminate them."

Astigmatism is the result of an asymmetric mirror or lens; a correct parabolic mirror shouldn't exhibit astigmatism. Is this correct? Is there a citation? MrDemeanour (talk) 08:42, 19 January 2023 (UTC)

The mirror is only symmetric on-axis-- at the center. Light which is off-axis encounters the surface asymmetrically. See the WP article on Astigmatism_(optical_systems)#Forms_of_astigmatism. --Gmaxwell (talk) 11:09, 23 April 2024 (UTC)