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

Here is the picture that I took: http://home.att.net/~krausefam/m13-100dpi.jpg

It is a picture of M13. I used Eta Hercules as a guide star, with a seperate guide scope and autoguiding web cam. The following diagram shows the direction of the star trail in the picture compared to what I was expecting to see since I was guiding on Eta Hercules: http://home.att.net/~krausefam/m13-chart.jpg

I thought that if the problem was bad polar alignment, that the star trails would rotate around the guide star, and that the guide star would stay still (by the way the guide star is outside of the picture), but in the picture I took, the star trails are not rotating around the star I was guiding on. The only reason I can think of for this is flexure.

Am I even right to think that a pure polar alignment problem (no flexure problem) would cause everything to rotate around the guide star?

Thanks,

Adam

----- Original Message -----

From: Stuart Heggie

To: Discussion of Film Astrophotography

Sent: Monday, August 29, 2005 9:42 PM

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

Adam, best if you can post a small pic you've taken so we can see what you see.

Stuart

----- Original Message -----

From: Adam Krause

To: astro-photo@seds.org

Sent: Monday, August 29, 2005 9:20 PM

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

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?

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?

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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