Re: [ATM] All Spherical Telescopes

["matt" <electro_optic@bellsouth.net>]

-----Original Message-----
From: Delyan Toshev <delyan@trirand.com>
To: atm@atmlist.net <atm@atmlist.net>
Date: Thursday, September 08, 2005 8:04 AM
Subject: [ATM] All Spherical Telescopes


>Hello,
>Noting the recent increase of topics about all spherical telescope
>designs, it is interesting to see a discussion about viability,
>perspectives and performance of such systems for the ATM community.
>
>Although some of these designs were already mentioned recently, the
>information and evaluation about practical implementations is laking. I
>find missing information about problem areas that are not obvious at
>first glance ( for me, at least ) - tolerances for surfaces, tolerances
>for centering and collimation, reflection issues, etc.
>
>It may be useful to make a list of known designs, and discuss the merits
>  and falls of each one. It will be very useful also to make some rating
>of such systems for visual, photographic or combined tasks.
>
>The designs and implementations known to me:
>
>- classic, all spherical Maksutov. The main goal Maksutov had, was to
>design an easy to build, yet high-quality school telescope, for that
>reason he looked at spherical surfaces as a must. I don't know, however
>which of the current production Maks are all spherical.
>
>- Lourie-Houghton variants, recently reappearing on the list :-)
>This design is known, at least in Russia, as Volosov-Newton, because of
>the work of russian optician Volosov during the 1940s on the same
>design. It seems he proposed it independently at the same time, as
>Houghton did.
>We know few of them were build, and some discussion already made clear
>more or less of their advantages and issues. Russian ATMers build some
>of these too, from 4" to 10" in aperture. One problem that is valid with
>LH is about its many air-to-glass surfaces. Any comments on this? How
>this can be overcome with relevant AR coating?
>
>- spherical catadioptric relay telescope. Sidler and Dilworth are known
>( to me ) were working in this direction. Still, very little information
>about practical implementation. One may conclude some difficulties for
>average ATMer to build some of the components of such telescope,
>particularly Mangin mirror, where there is one mirror-to-glass surface
>which is required to be polished to very low error - about 1/20 of green
>light. Another issue, which such system will present are the tight
>tolerances for centering and linear separation between elements. May be
>someone can bring more information on these issue as well to propose
>some remedy?
>Little is known about ATMers successfully implemented any of these. One
>commercial telescope is manufactured, based on same or similar scheme -
>the Clavius 166 - made in France by renowned optics company.
>
>- all spherical catadioptrics with sub-aperture corrector. Although this
>sounds like previous example, with relay lens-corrector, these are not
>quite the same, IMHO. Here I have in mind the design proposed by Klevtsov
>(http://www.telescopes.ru/articles/article1.phtml), which is implemented
>by russian company NPZ, the models TAL-150K, TAL-200K, TAL-250K (
>TAL-300K is planned ). It _appears_, that Vixen implements similar
>design for their VISAC and VMC200 catadioptric cassegrains, too.
>The work of Klevtsov is based on previous work of Argunov, another
>russian optician, who quit this direction of work some years before
>Klevtsov made his variant. As one can see, he also uses Mangin mirror
>and small meniscus as a system.
>Very controversal system, although it is interesting to separate design
>by given implementation. Still, it is interesting to know how this
>desing is viewed by ATM community.
>There are 2 Klevtsov type telescopes build in Spain with aperture about
>0.60m.
>
>As general note of interest is how the practical benefits ( if any ) of
>these designs relate to given aperture? It is my opinion that in case of
>relay telescopes and the Klevtsov ones, the aperture from 10" up is
>starting to look more and more interesting.
>
>Excuse me for the long post and my far from perfect english. Hope, I not
>caused a big suffer to the list :-)
>
>--
>Best regards,
>Delyan Toshev

There is also the larger Vixen VMC330 which uses an all spherical design but
the subaperture corrector gets more complicated . The smaller models use a
single meniscus , Maksutov style, the VMC330 uses a 2 lens corrector . Vixen
has some spot diagrams on their website but no optical prescription data.
And oh, sells for only $20,000 :
http://www.vixen-europe.com/htm/teleskope/reflektoren/vmc330l.htm

There is the Unicorn Project designed for NEO research , consisting of 3
Klevtsov telescopes of 61cm aperture (F/4) :
http://www.oam.es/unicorn/ninstrumental_en.htm

Their website says "BK7 of 18-cm of diameter. The corrector has been
designed for those primary mirrors and to obtain a f/4.0 resultant focal
lenght. The design and analisis of the optical has been performed by Mr.
Gerardo Avila, of the Optical Instruments Group of the European Southern
Observatory. (Karl_Schwarzschild-st. 2 85748 Garching, Munchen, Germany)
VALMECA S.A.R.L. (Serge Deconihout), Lantelme 04700 PUIMICHEL (France) taked
charge of the construction of the 3 correctors. They are already concluded."

best regards,
matt tudor



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