just like this robin?
http://i700.photobucket.com/albums/w...nal-HQ-AFC.jpg
Do you have a star field with a exposure of say 5-10 minutes that have small stars, I have always found that bigger stars like that don't show how round your actual star is. There is a great double star in the running man that gives you a very very good indication on roundness it also shows how good your resolving power is. the better your scope is collimated and the better its guided the better these stars split.
Alternitively CCDIS will give you a aspect ratio that is how round your star are, ill normally sit around the 10 mark with guided 10 min photos.