-----Original Message-----
Date: Tuesday, December 01, 1998 8:43 PM
Subject: Re: [M]: Re: Pointing /Polar Alignment Problem


Sorry for the long reply but I think we're onto something.

I'm not quite sure I understand your definition of parallelism. Let me
assume you mean that a line drawn through the center of the arms should
cross the center of the bolt holding the RA axis. OR put another way - a
line drawn along the DEC axis should pass directly over the RA center bolt.
I also assume that if the arms are not parallel then the symptom would be
that the arms would - if I was standing in front of the control panel -
BOTH be tipped toward me or away from me (albeit a small amount).

I also assume you mean the error would show itself as the cone of light
swimming around the center of the RA axis as you rotate the RA axis and If
the error was zero then the cone would be motionless.

I'm not sure this is true - I'm having trouble picturing this. I can picture
that if the arms aren't in line and this causes the cone of light to be off
center then I can see that it would scribe a circle about the axis as you
rotate the RA. BUT if the arms were tipped one way or the other and I didn't
know it, but I correct for it by rotation the OTA a bit in DEC to put the
cone of light directly over the center of the RA bolt then wouldn't the
cone of light stay there even if you rotate the RA axis?

Don't forget you are looking up a a sky that is evenly lit in all
directions. You are not looking at a point source of light. I think for the
cone of light to swim about the central RA axis when you rotate the scope
you would need to be looking at a the image of a point source of light
wouldn't you?

The question becomes then - how do you tell non-parallellism of the forks
(with the RA axis) versus a simple tube that is not exactly perpendicular to
RA (ie setting circle is off). The symptom of the light cone moving when you
rotate the RA axis would be the same for both faults wouldn't it?

Hmmm - we need to come up with another check for the problem of non-parallel
fork arms I think.

In any case I guess my arms were in line with the RA axis because aligning
the cone of light like I described REALLY fixed the GOTO problems for me.

SAGE


>A refinement just occurred to me. Your method assumes the fork arms are
>exactly paralell with the RA axis. If they are not, there can be some
>error. What about this slight revision....
>
>Place a white cardboard on the base over the RA axis as in your method,
>attached to the RA bolt so that it does NOT move when the scope is moved in
>RA. Concentric circles on the cardboard will help here too.
>
>Now, rotate the scope in RA only. Adjust the DEC and the OTA adjustment
>screws (and the fork arms if needed) so that as the scope is rotated in RA
>there is no motion of the light cone on the stationary screen.
>
>As far as I can visualize, the only way the image of the light cone can be
>stationary on the stationary screen as the scope rotates in RA is if the
>optical axis and the fork arms are precisely parallel to the RA axis.
>Keeping the scope pointed near vertical should eliminate flexure from the
>equation.
>
>Whatcha think?
>

View index by [date] [author] [subject]
Previous message: Re: [M]: OT:Telecompressor/Focal Reducer for Meade refractor, Paul Sterngold
Next message: Re: [M]: Pointing /Polar Alignment Problem, Bob Denny
Next message in thread: Re: [M]: Pointing /Polar Alignment Problem, Bob Denny
Previous message in thread: Re: [M]: Re: Pointing /Polar Alignment Problem, Paul Goelz