Field rotation??

Hi.. I was out last night photographing the beehive cluster with the 10D at prime focus with the lx200 10" GPS SMT. After developing the image I noticed that the stars at the top were round while other stars seemed to be in a circle. Was this problem caused by field rotation or maybe colmination. I am not using a wedge and I read in the manual that it may have been caused field rotation. Could someone please give me some advice on what the problem would be. Each image taken was a 2 minute exposure. I will include the image so you can see what is happening.

Attached Image:

Hi Ryan,

Your image displays both star trailing and field rotation. Thirty seconds is about the limit for alt-az for field rotation. And 30 seconds or less will take care of the trailing as well.

Of course you can then stack hundreds of 30 second frames to get a very good signal to noise ratio. Your aligning software must then both rotate and translate, but most astro image processing aps do this, some automatically.

Here are some 30 second stacks to give you a feel for what can be done.
http://home.att.net/~dpersyk/dso.ht
I used a wedge but my LX-90 tracking was only good for 30 seconds so I might as well have been in alt-az!

Clear skies,

Dennis Persyk
Igloo Observatory Home Page http://dpersyk.home.att.net
Hampshire, IL

New Comet Images http://home.att.net/~dpersyk/new.htm