Re: [ATM] Cassegrain vs. Gregorian (secondary testing)

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Bob May wrote:
 > The concave surface is between the spherical and parabolic surface 
and that
 > is easy to do.  More difficult is to depress a ring on the convex surface
 > and then be able to measure it accurately, especially since the curve 
is a
 > lot more than doing a parabolic surface on that convex surface.  I think
 > that you are thinking backwards.
 > Bob May
 > http://nav.to/bobmay
 > bobmay@nethere.com
 > NEW! http://bobmay.astronomy.net

It sounds like some of the problem here is simply getting the test setup
to actually come back to a focus in an easy way.

Question:
     Assume a desired system like (400 mm f/16 with a 20% paraxial
obstruction):

	http://users.rcn.com/rflrs/cass01-06.len

Suppose you just happen to have a 150 mm f/3 achromat laying
around (;-):

	http://users.rcn.com/rflrs/cass01-06t.len

I know there are a lot of questions here about accuracy and such, but
the question I have is about the amount of travel.  In this case, it
looks like about 75 mm (moving source).  Assuming your micrometer has
that much distance in it, is that too much travel to have faith in
the result or be unworkable?

-- 

Rick S.

http://users.rcn.com/rflrs


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