Even though it is not my main image processing software, occasionally I use the software ASTAP (Astrometric Stacking Programm, http://www.hnsky.org/astap.htm) for some purposes. ASTAP is slow (only uses one CPU!) and somewhat old-fashioned, but it has great features for analyzing images with aberration problems, for example due to tilts of the image train. Furthermore, its free and there is a Linux version, which great !
The aberration inspector of ASTAP (keyboard shortcut “F7”) creates a mosaic of nine small images of the four corners, the four outer midsections and the central section of your image. With such a mosaic, it is very easy to judge the quality of your optics and of the adjustment of your optical train. Here is an example view.
