Talk:Maksutov telescope

From Wikipedia, the free encyclopedia

I have several gripes/questions about this page

1. I don't believe that it is appropriate to link to "Schmidt corrector plate" because the Mak uses a thick "correcting lens", not the thin plate with the manufacturing process described on that page. Does this lens effect magnification?

2. Mak's don't suffer from chromatic aberration? Chromatic aberration occurs because curved glass bends different frequencies of light different amounts, and Maks have a big curved piece of glass in the front. It isn't possible to fix that with mirrors which are suppposed to deflect all light at the same angle. I'll buy that it's significantly reduced since there's little focusing going on, but the claim of none is probably erroreous.

3. The comparison to the Schmidt is probably incorrect. Ritchey's have a hyperbolic secondary mirror; I've never read anywhere that Schmidts do (most sources simply say convex). The new RCX Meade telescopes use a spherical primary, a corrector plate and a hyperbolic secondary mirror and are called Ritcheys.

---

To partially answer your questions:

The Schmidt corrector plate is indeed quite different in form and function from the plate used in Maks. It does not effect magnification apart from the contribution it makes to the overall focal length of the optical system. However the SCT and Mak are the only two mass market catadioptric telescopes available to amateurs. To the layman they are very similar in appearance and share an light path that is dissimlar to that in most other designs. Therefore the link to the SCT page.

The Ritchey-Chretien design also has similarities but is not a mass market telescope. The Hubble is a true RCT the Meade design is adapted to include a corrector plate, and therefore is unique. All other Ritchey-Chretiens are not catadioptric designs.

While it is technically the case that there must be some chromatic abberation in the MAK and SCT designs, this is only the case in telescopes that have sub-standard optics. The corrector plates in both designs do not substantially change the light path, their main function is to adapt the light to suit the optical characteristics of the primary mirror. In other words there is not much refraction going on. The light is mainly focused by the primary mirror. I have looked through three different makes of Maksutov, including a small Chinese one. The moon against a dark sky exibits no discernable colour on either limb, and I was looking for it.

their main function is to adapt the light to suit the optical characteristics of the primary mirror

can you explain that a bit? I have no idea what sort of adapting might be needed or useful Funkyj 00:07, 19 March 2006 (UTC)

Contents 1 Cleanups 2 Not an ad 3 Off axis coma 4 More cleanups

[edit] Cleanups

I have cleaned up this page a bit. It had information that seemed to repeat several times in many different paragraphs (probably do to piece meal editing over time... everyone adds the bit they know ;^)). I borrowed the layout of the Schmidt camera page as a model and arranged most of the info into a more coherent structure.Halfblue 22:03, 25 September 2006 (UTC)

[edit] Not an ad

No, really not. There's a reason why so many different optical systems exist: they all have their unique characteristics,their advantages and disadvantages. The questions discussed in the article are relevant, and the facts mentioned are well known. See for example Rutten and Venrooij's "Telescope optics", the de facto standard handbook where such matters are discussed extensively. Kosebamse 14:44, 2 April 2007 (UTC)

The problem I am citing is a lack of citation. You can write anything and claim you know it but one of the tenants of Wikipedia is everything should have a citation. This paragraph has a lot of "claims of superiority" that read just like an advert. Its a common problem I come across editing a lot of Wiki articles about telescopes - people quote the material from commercial advertisements and think its a valid reference (which it is not for many reasons). If there is a citation to back this up then you should add it.Halfblue 17:42, 4 April 2007 (UTC)

[edit] Off axis coma

The opening line of this article reads The Maksutov is a catadioptric (mirror-lens) telescope that is designed to minimize off-axis aberrations such as coma.

The Maksutov has strong off-axis coma. See Telescope Optics, Rutton & Venrooij p.103-105. Am I missing something? --Duk 07:23, 3 April 2007 (UTC)

the intro should probably be something like; The Maksutov is a catadioptric telescope design that uses all-spherical elements, thereby simplifying fabrication. It is diffraction limited on-axis and has good color correction. Variations on the design with aspherical elements can reduce off-axis aberrations such as coma. --Duk 07:53, 3 April 2007 (UTC)

It's a wiki. Feel free to improve it. Kosebamse 15:36, 3 April 2007 (UTC)

I have re-edited the intro since an intro should hit on the most notable aspects of the "thing" in question. "Fabrication" was not the notable reason for the original design... in fact Maksutovs are hard to fabricate. Dmitri Maksutov's intent was to correct spherical aberration (supported in now cited reference). This was similar to Bernhard Schmidt's attempt to correct for the same problems in the Schmidt camera. I don't have the ref Duk was talking about but we may be mixing the modern Maksutov Cassigrain with the "original" design. Maksutov Cassigrains are not built on Dmitri Maksutov's design since the corrector is moved down to the focus of the mirror. This is propably what introduces the off-axis aberrations noted. As the article says "Gregory himself, in a second, faster (f/15) design resorted to aspherization of the front corrector surface (or the primary mirror) in order to reduce aberrations." Halfblue 16:26, 4 April 2007 (UTC)

Yes, that agrees with the my ref; all-spherical elements were not noted as the driving force behind the design, and the "strong off axis coma and astigmatism" was noted for Gregory's 1958 f/15 design. --Duk 18:32, 4 April 2007 (UTC)

A little addition - I think this introduction is true:

"The Maksutov is a catadioptric telescope design that employs an all spherical primary mirror and concave lens to correct the problems of off-axis aberrations such as coma found in reflecting telescopes wile avoiding chromatic aberration[1]. The design can be used in a cassegrain configuration, thereby simplifying fabrication. There are also designs with aspheric or additional elements to reduce off-axis aberration in the cassegrain designs."

need to hit the references to find full citations. Halfblue 18:39, 4 April 2007 (UTC)

Out of curiosity, are Maksutov's at all common? or are the consumer products mostly of the Gregory-Maksutov design? --Duk 18:57, 4 April 2007 (UTC)

Almost all Maks I have seen are the spot-mak Gregory design. We did build a one-off custom very large (16") Mak that was non-spot-mak at the shop I used to work at. It was similar to Maksutov's original design with the corrector outside the focus and was convertable from cassegrain to newtonian. Halfblue 13:34, 5 April 2007 (UTC)

[edit] More cleanups

Moved Maksutov Cassigrain down to Derivative Designs. I am wondering if the Klevtsov-Cassegrain belongs in this article since there are other designs that use lenses ahead of the secondary in an attempt to correct aberration (such as the Argunov-Cassegrain telescope) and maybe the Klevtsov falls in that catagory. I do remember reading a ref that the Klevtsov was a Maksutov derivation durring a previous cleanup but I didn't cite it (hey... do as I say, not as I do ;^)). Halfblue 18:21, 4 April 2007 (UTC)