[ATM] ATM - Schiefspiegler!!! - (really a question about lens curves)

[Adam Perkins <scopeguru@yahoo.com>]

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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