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

[Michael Peck <mpeck1@ix.netcom.com>]

At 13:35 28-08-04, Richard F.L.R. Snashall wrote:


>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?
>

There are lots of good null tests for cassegrain secondaries, many of which 
I'm sure you know about. If not, there are numerous examples on Peter 
Smith's web site, a few in Texereau, at least one in ATMT (vol. 1), a dozen 
or more in Wilson's "Reflecting telescope optics, vol II".

The secondary in your .len file only has a couple waves worth of spherical 
aberration relative to a sphere (if I did the arithmetic correctly). You 
could probably get away with doing a simple interference test against a 
spherical test plate, especially if you use FringeXP to do quantitative 
data reduction.

Mike Peck


------
Michael Peck
mpeck1@ix.netcom.com

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