[NightCal]

My present imaging set up produces a degree of field curvature. What I need is a field flattener. The trouble is that equals money and at the moment I don’t have as much I want for buying astro stuff. (do I ever?)

Looking at the effects of field curvature on the image it strikes me that this looks very similar to star trailing, except that the direction of trailing varies with angle and the amount of trailing varies with distances from the centre.

Now, I know that there are several different ways of removing star trails in Photoshop.
http://www.focusmagic.com/
http://www.sightsabove.com/article.php?article=20
http://stargazerslounge.com/imaging-tips-tricks-techniques/113075-startrail-remover-ps-action.html

and probably many more I don’t know about.

So, is there a way of applying any of any star trail removal techniques so that the degree of star trail removal varies with distance from the centre and the angle of trailing removal rotates around the image?