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"Ian Peterson" wrote in message
nk.net...
I have a 14" Celestron SCT that I suspect has some sort of optical
problem
like spherical aberration. I can't realistically expect to do a good
star
test due to poor seeing in my area, and I lack the necessary distance to
place an artificial source. This beast is HEAVY and setting up on a
regular
basis only to be disappointed due to lack of stellar diffraction
patterns is
getting annoying at the least. The other day, a friend suggested
removing
the mirrors for bench testing. Although I have had the scope apart
before
(after first correctly nothing the secondary, primary and corrector
positions), I have never removed the mirrors although I don't think it
would
be too difficult a task. I have a couple of questions: 1) If I were to
remove each mirror for testing indoors, what equipment would I need?
Does
standard "mirror making" test equipment work with SCT mirrors? 2) Would
I
even have to remove the primary or could it be tested from within the
tube?
3) Has anyone else done this type of testing and can you provide a link
for
guidance?

Thanks in advance. BTW, this scope is 6 years old and was purchased
used.
I don't think the original owner realized that there was a problem
having
always done wide field work, however I don't know that with absolute
certainty.

Ian


Ummm, if the seeing is so bad that you can't do a star test (which means
you can't collimate it properly either), what leads you to believe you
have problems with your optics?

Your problems may well be related entirely to your poor seeing, and quite
possibly also to lack of collimation. And you have said nothing about
what you are doing to ensure your scope is reaching thermal equilibrium,
which for a scope this size, and this configuration, will take a LONG
time, unless you have supplemental cooling equipment in use. And, if your
scope is not fully equilibrated, you are not going to have a good star
test, regardless of seeing OR collimation...

Before you can begin to evaluate your scope's optics, you MUST be looking
through a critically collimated, and fully equilibrated telescope...

Finally, if, as you state, your seeing is consistently bad, all the bench
testing in the world isn't gonna' get that scope to perform any better if
it's always seeing-limited...

Perhaps before you start taking the scope apart again, you should take it
somewhere that DOES have good seeing, and try it THERE. And better yet,
do this with someone present who's familiar with the care and feeding of
SCT's... THEN decide if the scope needs further evaluation