RE: [ATM] ATM Schiefspieglers in Oslo EDU - updated

["Donald Good" <donald.good@comcast.net>]

 Hi Jerry,

I was surprised, too.  In looking for "something else", do you mean for
another design, or for another item in this design that will make it not too
good to be true?

If another design, there may not be another that is better across the full
field that presents such a small spot relative to the Airy disk.  And no
obstruction, too.

As for this design, there are a few limitations.  The focal plane is tilted
which may present some dificulties in focuser design.  There is a limited
range of F numbers that make it practical.  Outside that range and the
errors start to rise again, or the length starts to increase relative to
diameter.  As far as construction, 3 surfaces need to be matched to a high
degree and holding the second mirror in collimation at the upper end
requires a very stiff structure, beyond that of a simple diagonal.  If
portability is desired, then the aperature is limited by the stiff
structural requirement which is at odds with lightness and portability.

However, having stated that holding collimation is a serious issue, I am
going to turn around and question that assumption.  Because the second and
third mirrors are spherical, they have a universally symetric characteristic
that may, in practice, translate into a kind of "automatic-collimation" even
as the structure flexes.  While the structure flexes within limits, the
actual parameters (effective tilts mostly) will change, but due to the
spherical mirrors, the vast majority of the mirror surface areas will remain
in collimation.  If the second and third mirrors are slightly oversized,
then the total primary aperature's output should find the focus, although
with slightly different tilt values than the design tilts.  The question
that needs further study is how much these changes affect the performance.

Clear skies,
Don Good

-----Original Message-----
From: Jerry [mailto:wa4guu@verizon.net] 
Sent: Monday, June 14, 2004 2:25 PM
To: 'Jerry'; 'Donald Good'; 'Richard F.L.R. Snashall'; 'ATM'
Subject: RE: [ATM] ATM Schiefspieglers in Oslo EDU - updated

And I see OSLO is set for inches. Do I seem surprised? Hmmm let me go look
for something else. It can't be that good!

Jerry

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