A local (Australian) astrophotographer recently did such a wonderful widefield rendition of the Eta Carina neb and IC2602 star cluster (with an SBIG 11000 and Tak106FSQ) that I wondered how I would go with a mosaic in the same area. Mosaics have long been on my "To Do" list, so I roughed out an imaging plan to collect 6 frames in this area (which eventually turned into 8 to fix up gaps and extend the FOV). The Newt and QHY9 usually have a bit too much resolution per pixel (about 1.1 arcsec/pixel) so I resorted to 5 x 3mins binned x 2 RGB for each frame, thinking this should be enough to give a half decent result if I succeeded in knitting it all together, but wouldn't take a silly amount of time to collect if it was all a disaster!
I spent almost 2 weeks figuring out the various (wonderful) PI tools for mosaics, eventually resorting to Dynamic Alignment against a StarGenerator artificial star field for individual master frames which I then knitted together in the auto mosaic mode (Register/Union - Mosaic) to take advantage of frame adaption. After convincing myself I could build a pretty good red mosaic in this fashion I then dynamic aligned individual frames for the green then blue data before again knitting those together using Register/Union-Mosaic, then finally Dynamic Aligning those assembled green and blue mosaics against the red frame (effectively using it as the reference). I was surprised at the relative rotation of the 2 columns of frames at assembly, although reading more know realise this is simply reflecting the "curvature" of the sky being represented by adjacent flat sub-fields.
The RGB image was then stretched using HTF, colour corrected (Rogelio's median technique and some manual tweaking to taste), some star Morphological Transformation to soften the stars, colour saturation and contrast adjustments, then final cropping. The assembled RBG mosaic before the above processing (and other JPG images in greater resolution) can be seen at:https://picasaweb.google.com/UserRobF/RecentWork#5580564329431758866
The green frames were the most problematic to get a flat field for (even with Frame Adaption), and unfortunately I had to collect more green and blue data around Eta Carina itself ending up with slight rotation in the spikes on that brightest star. I'm still very happy with this output for my first serious multi-panel mosaic, and all the more in awe of some of the great PI functions for doing these. Definitely won't be my last mosaic, but for now need a bit of a break from this one before considering doing anything else to it (I honestly think I've spent a couple of hours on it at least every night for the last 3 weeks now - it became that addictive).