Re: [ATM] testing an f/2.6 mirror?

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

Guy Brandenburg wrote:
> Somebody wants me to test test an f/2.6 mirror, (8 inch diameter)?
> Sounds to me like something one would need a wire test to do, and
> I've never done that before. Any thoughts? Guy

Interesting coincidence.

I bought an old 8" F/2.6 mirror recently.  For the price, I didn't 
care what the figure was - the generated, polished, cored blank itself 
was worth the money.  I think it was from some old Edmunds cassegrain 
telescope.

I used a pinhole test (with a beamsplitter) to check for figure of 
revolution and it showed a large amount of very bizarre coma-like 
distortion even though I was testing exactly ON-AXIS.  Back to a 
sphere for this one!

If this other 8" F/2.6 mirror is similar in manufacture, then my 
advice is to give it a quick check with a pinhole first to see if 
anything strange is noted.  Alternatively, put it in a crude tube with 
a secondary and see if star images are reasonably round.

	Mike Lockwood

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