I don't know what the difficulty is but PI seems very picky about what settings are selected in order to register data from widely differing image scales- I tried previews, thin splines and nearly every combination of settings I could think of and mixed images would not register. Image from the same camera okay but mixed images not having it.
However I found a great software suite that I've just purchased which is solely dedicated to star registration and processing. It is a bit quirky and the interface could be a bit more modern however it works really well. Just set any image of any image scale as the master (even OSC bayered) and it works against a full folder of 16 bit images and churns through them in sequence. It even calculates and corrects the image distortion between different optical systems and compensates forthwith- so I've read in the help files.
I also had an earlier copy of CCDStack however this software really makes that look like a freebie!
I'm using this software to build my NGC3718 image as there are 2600 subs imaged through 3 camera and 2 telescopes with widely differing image scales. The software costs $175.00 however it is well worth the money. You can get a trial copy to play around with however its not much use as you can't save any output so you need confidence that it works and bite the bullet as they say. The only small limitation is that the software works at 16 bit- it is supposed to correct 32 bit images to 16 bit truncation but I could not get that to work so I've resampled my entire data stack to 16 bit.
I've only tested a small data subset of 20 of the registered images however its looking very good as the sample came from 3 different cameras and I see no differential distortion verses distortion seen at the edges of the masters when I tried to integrate the 3 seperate camera stacks through PI.
The link is here https://aurigaimagin...al/ordering.php
Edited by pyrasanth, 20 April 2021 - 11:22 AM.