[JohnG (John)]

Hi Paul

Your effort was pretty good for a first try. As you have already found out, you are going to be limited because of your Alt/Az setup. I have no experience using Alt/Az to photograph, I use a GEM. Unfortunately, using a guidestar in that mode will still cause field rotation.

If you have a look at each corner of your shot (blown up) you will see what is known as Field Curvature, unfortunately a problem when using an SCT, you may be able to get away with slighly longer exposures using a Focal Reducer, this will make the image size smaller but you may be able to crop the image to get rid of the curvature.

Someone with a bit more experience with SCT's may chime in and give some advice, I use a refractor to image.

Cheers

JohnG