[ATM] Al Spherical Telescopes

["Gianluca Carinci" <g.carinci@tiscalinet.it>]

Hello,

I've seen the Dilworth described on "Advanced Telescope Making Techniques"
by Mackintosh (collected Mackintosh Club Circulars). Dilworth at his first
attempt used a primary Mangin and a quite step by step "try and re-try"
method (at least, he told so: he built his relay telescope after having
found some high index small lenses in a closing optical shop).
His second one (a 16") used a Mangin secondary and was better studied efore
starting with grit.
Both of them won price for excellence in optical design and mechanical
construction at Stellafane (in the '70s)..

The sensation is that it offered high performances, but with a quite small
field.

The Klezov is, conversely, an interesting performer when it comes tyhe need
for a (quite) large format camera: at least, I have read careful evaluation
of two different OTAs (8", two differebnt owners), and the performances were
nice, but lower than the one allowed from a C8 (on planets it th Kl. seems
to show colors).

A small firm here in Italy is now producing an all spherical photographic
camera (a nice assembly, without tube: similar to the Dilworth, but without
relay systems, for what I know).
If I have well understood, it uses a secondary Mangin or a secondary with a
corrector just in front of it (I do not know exactly ).

I know by person the designer, but allow me to say that I have absolutely
not any interest in speaking of him: I have just re-met him with his setup
at the (just ended) Saint Narthelemy Star Party here in Italy.. and had no
time to take a peek: here was a cue and it was.. dark (for this I do not
know much about the design: there I had no time to ask more and to look at
better).

If I'm allowed (and asked) I could post on the ATM forum the firm name and
the designer's web address.

By the way, the Mackintosh book is quite interesting in noting differences
between today and "gone times" design approach...
It describes also Lurie Houghton...
I have only the last fifteen or so ATM journals (not here), and I do not
know if on the Telescope Making magazine there was something on this matter.

By the way: there is a reprint of the Telscopepe Making Magazine somewhere ?

Gianluca Carinci
Rimini, Italy



----- Original Message ----- 
From: "Delyan Toshev" <delyan@trirand.com>
To: <atm@atmlist.net>
Sent: Thursday, September 08, 2005 2:03 PM
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
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>


_______________________________________________
ATM mailing list http://www.atmlist.net/