You may recall I did my first proper mosaic recently (Flaming Star and Tadpoles), I merged it in Photoshop but it was quite a job.
Then some-one on Astrobin told me about ICE (Image composite Editor). It's absolutely brilliant, it combines the pieces of the mosaic in a flash and seems to even out the colour differences.
I don't know when I am likley to use it again, but thought I'd post this up in case it helps any-one else. I recall Duncan you did a mosaic once of M45 and had difficulty combining.
It's free as well.
https://www.microsoft.com/en-us/research/product/computational-photography-applications/image-composite-editor/
Carole