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

On 8/29/05, Adam Krause <krausefam@worldnet.att.net> wrote:

Hello,

I'm new to the group and am starting in film astrophotography. I have taken some shots at prime focus and have noticed star drift. I am autoguiding with a webcam on a seperate guide scope.

Right now I am assuming that if I am autoguiding on a star, then if my polar alignment is off, the field of stars would rotate and trail around the guide star, with the guide star standing still. Is this correct?

Yes, this is correct. But the reverse is not always true.

I am also assuming that if my star trails aren't rotating around the guide star, that this is because of flexure between the guide scope and the main scope. Is this correct?

Yes, this is due to flexure. But it's always difficult to hunt down

which part of your system is the source of flexure.

I am trying to see weather my trails are caused by poor polar alignment or flexure and if my second assumption is correct, then I need to work on the flexure between the scopes.

Thanks for you help,

Adam

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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.

Wei-Hao

--
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Wei-Hao Wang  :)

Institute for Astronomy at University of Hawaii

Address:
2680 Woodlawn Drive         Personal Website:
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