Re: [ATM] ATM - Schiefspiegler!!! - (really a question about lenscurves)

["David Harbour" <stainless_steel@suddenlink.net>]

Adam,

See my later reply to your post. You can find what you need at your local 
vending optician, right there in town. However, I am very apprehensive that 
it would introduce astigmatism into the system; but I am fond of thinking of 
ways to "filter out" astigmatism; it could be done with the primary, a 
little retouching.

I once corresponded with Sherman Schultz (yes- the legendary Sherman Schultz 
who taught telescope making at... McCalister college, in the twin cities 
(one of them). This, so long ago, I actually had to use a typewriter and 
paper.

We had written, dialogued about how was the best way to remove astigmatism 
in a Newtonian, where the primary was astigmatic; I told him that I would 
like to try a little "Yolo" style warping harness on the diagonal; however, 
he said he preferred a tilted lens- perhaps a meniscus of zero power.

Perhaps you could include a tilted lens of zero power into the system, and 
it would still be unobstructed? Double pass, though.... Hmmm....

Interesting proposition of yours.

R-101

----- Original Message ----- 
From: "Adam Perkins" <scopeguru@yahoo.com>
To: <atm@atmlist.net>
Sent: Monday, April 14, 2008 9:41 PM
Subject: [ATM] ATM - Schiefspiegler!!! - (really a question about 
lenscurves)


> Hi everybody,
>
> I got into my head last night to work out the
> feasibility of a Schiefspiegler scope cobbled together
> from common surplus parts.  See
> http://telescopemaking.org/schief.html for an example
> of what I'm envisioning.
>
>
> My Idea:
>
> The Primary:
> Get one of those 4.25" f/10 spherical mirrors that are
> available so cheaply, and mask it down in aperture to
> meet the needed f-ratio of the final design.
>
> The Secondary:
> Find a surplus lens with an exposed convex element of
> the right radius, and get it aluminised.
>
>
> I don't how common a convex element of +/- 80" radius
> might be, but I'm hoping someone can point out a
> correlation between EFL and curvature of exposed
> elements in a "typical" achromat.  A simple lens would
> be ideal, but beggars can't be choosers in the surplus
> market.
>
>
> This all brings me around to my real question...
>
> What problems might arise sending a cemented doublet
> into vacuum coating chamber?  Melting or outgassing of
> the cement?  Separation of the elements?  What about
> AR coatings in the same environment?
>
>
> If I can get my hands on a suitable convex element,
> I'll spend some time with WinSpot and see what's
> possible.
>
> It seems to be a part of my nature to find things that
> do well in their designed application, and cobble them
> together into something worse...
>
> Adam
>
>
> 
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