[gregbradley]

Mosaics are hard. Plan it out carefully.
The main thing is to make sure each panel gets the same exposure details as closely as possible and the same conditions, same exact focus, same filters, same scope, guiding etc - all the same as much as possible. Trying to take all panels in one night may cause differences. Approx the same time each night for each panel would work better but may not be practical. 2 panels a night I found workable. 2 hours per panel or less makes sense. How often do you get 4 or 5 nights clear in a row with similar conditions?

Process each panel exactly the same way up to a basic LRGB image. Stretch each one the same amount so one panel is not stretched differently to the rest. Thats what looks like happened here with your image. One is processed differently to the others or was taken under different conditions or exposure lengths etc. Don't try to finish processing them separately. Be methodical and consistent and take each panel to a basic LRGB image, then stitch them and then final process for colour.

Photoshop whilst improved greatly in CS4 is still a weak mosaic tool. It does not do a great job of balancing out the panels nor the overlaps which are often quite visible requiring time consuming fiddling that does not end up with a very good result. Other software is better. Microsoft ICE is free, PTGui Pro is good. You may need to manually stitch some shots as PTGui for example does not like star scenes. You may need to reduce your panel images so the software can handle them easily.

Its easier to get the acquisition right than try to fix it in post processing which is nearly impossible to do. Also allow a bit more overlap than you would think is needed. 1/4 would be a minimum overlap.

Pixinsght is another approach. It would take a learning curve as last I used it the software was complex and you needed to be precise. They have refined it but I have no experience in how it is now. I suspect its still hard to use.

Greg.