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Re: [ATM] Aplanatic Gregorian: A FORMULA (was: 25" mirrorpossibilities)
Here's a formula that I worked out using SpotPlot (or
was it WinSpot?) In either case, Gregs can be
aplanatic like the R-C Cass, though the tube length
will get long enough to consider the Newtonian RFT and
a telextender lens setup.
Primary: 336mm Dia. 2095mm ROC -.9915 CC
Secondary: 73.625mm Dia. 366mm ROC -.5495 CC
Pri - Sec distance: 1260mm
Sec - Diag dist: 1000mm
(Yes, it's a coude)
Field size = .25* (half a full moon)
f/D is 19.34
Field diameter = 28.35mm
Coma S' = -.000002 Coma T' = .000005
Ast' = .167755
These values are the central values; it is nearly
impossible to hold tolerances like these without an
advanced machine shop. But if you can do it... I
dare you. :-P
To hold the secondary I suggest using an optical
window. This will stop the second set of spider
diffraction lines from forming. But if a fine wire
spider stops the spikes, don't use a window.
Kevin of Eastern Iowa
Seeker of the Darkness and Perfect Telescope
--- lou krajci <loukrajci@comcast.net> wrote:
> >From: Michael Peck <mpeck1@ix.netcom.com>
>
> >...Unfortunately the standard ATM
> >reference on telescope design (R&vanV) doesn't
> discuss Gregorians in any
> >detail, so most ATMs don't realize they are
> basically the same class of
> >telescope.
>
> Bingo. My point exactly.
>
> >Modern texts like Schroeder's "Astronomical Optics"
> or Wilson's "Reflecting
> >Telescope Optics" treat all two mirror designs as a
> single family. Neither
> >of those are aimed at ATMs, but in my opinion every
> serious ATM should own
> >at least one of them.
>
> At around $100 each? (And isn't Wilson's book in
> two volumes?) Ouch.
> That's a big price for many ATM's.
>
>
> >From: Mauritz Andersson
> <mauritz@physi.uni-heidelberg.de>
>
> >For those of you with access to Applied Optics
> journal,
> >the following is a great reference on two mirror
> aplanatic designs.
>
> >Rimmer, Wetherell
> >"General Analysis of Aplanatic Cassegrain,
> Gregorian and Schwarzschild
> >Telescopes," Applied Optics, Vol. 11, 1972, p.
> 2817.
>
> Another big price for the average ATM.
>
> While the suggestions above are well-intentioned,
> they won't help any but a
> few hard core ATM's. Where does that leave the rest
> of us?
>
> I will keep studying Mike's spreadsheet...and then
> ask him some questions
> about symbology and how to use it to whip up
> aplanatic Gregorians. If
> nothing else...maybe we can come up with some
> simplifications/rules of
> thumb...some starting points and examples for ATM's
> to start from.
>
> Tom Krajci
> Albuquerque, New Mexico
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