On Wed, 6 Apr 2005 RichardN22@No-Spam wrote:
>
> Richard Ozer has probably taken part in literally hundreds of star tests of
> mirrors at the Chabot Observatorys telescope makers workshop where he is an
> instructor.
Didnt mean to offend. It just sounded from his email he had little
experience with artificial star testing, which is what you use for the
normal figure-test-figure-test cycle.
> I wouldn't consider a person who kicks the rocker box as a means of
> collimating a '
> serious tester.' Not to say he hasn't done an incredible service to the
> amateur community.
That has nothing to do with his expertise at figuring a mirror by the star
test, which he is darn good at!
> Are you saying that the star test is the only way a person should check a
> mirror that they are figuring? There are many variables introduced when you've
> got a mirror installed in a scope that could introduce errors in a star test.
> Yes, a star test is a great and important way to test a system, but in my
> opinion, a carefully conducted test of a mirror will give lots of useful
> information, especially if you're grinding your own mirror.
>
Its not the only way, of course, but it is the final arbiter of the
mirror's quality. And its best to finally test it in its actual mounting
and OTA anyway. Its obvious what you see in the eyepiece must be
perfect, that is the standard you are trying to achieve. Doesn't matter
what a wire, ronchi, foucault, Hartman, null, interferometer says, if its
not a perfect pattern at the eyepiece, its not acceptable. In fact, in
many cases these indirect tests say the mirror is perfect, but the star
test gives a completely different answer! Yes, you can use other tests as
a guide for rough figuring, but be prepared to do the final testing at the
eyepiece to be sure you have it right.
Mike
Received on Wed Apr 6 10:54:02 2005