Image Artifact Problems

[bricks1000]

Hi, I've not been imaging long and am still using a CPC tracking in Alt/AZ (until my wedge arrives in the next couple of weeks.

I keep encountering the same problem in all my images taken so far. concentric circular artifacts/smudges which resonate out from the middle of the image.

Here is a link to a recent example taken a couple of days ago.

http://www.flickr.com/photos/80299219@N08/7813679326/in/photostream

The larger the image is viewed, the more apparent the problem is, looking at the middle of the nebula you can see a point where the circles start to resonate outward.

This particular shot is a stack of around 40 frames at 45 secs each stacked in DSS, I use 2 or 3 dark frames usually, shot through a modded 1000d with astronomik cls ccd.

Any help in identifying what is causing the problem will be much appreciated.

Regards,

Graham.

[Cornelius Varley]

I'm not sure what the problem is. At first I thought it might be field rotation or coma ( the stars look enlongated at the edges of the image).

Peter

[bricks1000]

Peter, you are right, field rotation it is. I didnt realise how pronounced it was when you image close to the zenith with alt/az. Luckily I recieved my HD Pro Wedge today (good service from FLO) so I should'nt have the problem any more (providing of course I can figure out what I'm doing with regards to using the wedge).

Graham