precision of ap900 gto


visonneau-vincent <visonneau-vin@...>
 

Hello from france (sorry fro my poor english)
I just receive my new mount 5 days ago (ap900 gto).I make some try this week
and i have some problems with precision pointing.What kind of precision can
we expect with that sort of mount.
I have a celestron 8" and the scope and the mount are connect with a system
who seems not very good for "orthogonalite".Perhaps the bad precision coming
here.
Bye
Vincent
France


Derek Wong <dawong@...>
 

Hi Vincent:

I just receive my new mount 5 days ago (ap900 gto).I make some try this week
and i have some problems with precision pointing.What kind of precision can
we expect with that sort of mount.
I don't have exact numbers, but if everything is right the precision can
be outstanding, within a few arcminutes or better.

I have a celestron 8" and the scope and the mount are connect with a system
who seems not very good for "orthogonalite".Perhaps the bad precision coming
here.
There are several issues:

1. Polar alignment may be off - you can check this with the polar
alignment scope or star drift tests.

2. The scope may not be orthogonal to the mount - in the manual there
is a method to check for this on p. 21-22. SCT's have mirror shift,
which may lead to more problems. Also, recollimating the scope will
change the relationship between the tube axis and the optical axis,
again affecting orthogonality.

Assuming your polar alignment is accurate, you may need to collimate the
scope, focus it on a star, then shim the rings if necessary and then
test the pointing.

Sorry, I'm on vacation and will not be able to respond until 8/1.

Derek Wong
dawong@earthlink.net