Re: Star Test Question
Chuck Grant (grant@aretha.llnl.gov)
Tue, 2 May 95 02:24:55 -0700
> From: "Mark VandeWettering" <markv@tick>
>
> I disagree for a couple of reasons:
> 1. Star testing is actually pretty simple, and Dick Suiter's book
> has made it even simpler.
> 2. Star testing is the only way for the average amateur to test
> the ENTIRE TELESCOPE. Ronchi testing at the ROC won't cut it.
> For newtonians, it doesn't tell you a thing about your diagonal.
> 3. Sure, autocollimation is good, but even I don't have a good flat,
> and I am obsessed by telescope making. :) Also for large mirrors
> this becomes more expensive.
> That aside, I think the best method is to use ALL methods, and try to
> figure out what each is telling you about your mirror.
>
Mark,
Given that we are talking about the star-Ronchi null test at focus, not the
at center-or-curvature test, what are your thoughts? It tests the entire
telescope and is easy for the amateur to construct and operate. I tend to
agree with what Rich Combs said, the test doesn't seem very sensitive and
most telescopes seem to look pretty good by this test. Of course it is
as difficult to use this test while figuring, as the both-sides-of-focus
star test, since you have to put the mirror into a telescope to do the
test (and usually you can only test on clear nights).
Chuck