Re: [APML] Polar alignment vs. flexure star trails

["Adam Krause" <krausefam@worldnet.att.net>]

Thank you William and Wei-Hao for you help on this subject.  You have both
helped me narrow down a little further the cause of the star drift, and I
like the idea of two high powered eyepieces on the same star.  It would be
neat if I can get another webcam and put one on the guidescope and one on
the main scope for testing.

My telescope is a home built newtonian 5" aperture, 1040mm focal length
scope on a horseshoe equatorial mount.  I have built a Mel Bartels drive
control system.  The guide scope is an inexpensive Meade 60mm, 700mm focal
length refractor.  I am guiding using a long exposure modified Creative EX
Pro web cam and K3CCD tools.

I was thinking there likely was flexure because the guide scope is not
attached very rigidly.  It is just the top section of the Meade tripod
attached to the main scope.  I will have to make something like guidescope
mounting rings to make the setup more rigid.  I would consider this my main
source of flexure.

I wonder how my secondary stacks up against standard secondary mirror
systems.  It is a hacksaw spider system (if you've ever heard of that), and
the secondary mirror is held in place by four 1-1.5 mm thick drops of
aquarium sealant.  I'm not sure how other secondary mirrors are held.  If
others are held by clips, I suppose they would be more prone to slip.  Mine
won't slip, but the sealant isn't "rock hard" either.  Don't know how much
that would matter holding such a light mirror anyways.

Thanks again for your help.

-Adam



> Not exactly ...... Movement of the optics can be a killer too. It might
> help to know what the primary instrument was and the guidescope ? SCT's
> and Newt's don't do guidescopes very well. Not with going to a lot of
> detail to secure the moving mirror (SCT) or the secondary (Newtonian).

>From the picture you provide, it seems pretty like a polar alignment
>problem.  However, this doesn't rule out flexure.  There is one way
>to see if flexure is a problem in your system.  Point both the telescope
>and the guide scope to the same star and put high magnification
>eyepieces on both of them.  Use either one to guide.  If there are
>flexure problem, you will see the star drifting away in the other scope.
>This can tell you if there is a flexure problem or not, but doesn't tell
>you where the problem comes from.

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