Hi Peter,
That's nice and I can see the improvement.
I did plug your photos into CCDInspector. Ideally you need to use a star field and not have a galaxy centered, but the results show that you still have some curvature and you also might have some alignment issues.
If you don't have CCDInspector it's worth a download and try out of free trial. I've found it to be an indespensible tool. With this tool you can quantify your experimentation.
Peter
http://www.ccdware.com/products/ccdinspector/