[IanP]

Thanks Rick and Pat.

You’re probably right Rick, if you integrate all subs or integrate integrated images – mathematically speaking it shouldn’t matter, but what if you first process each of integrated images and then re-integrate them and “polish” the resultant photo?

Pat, I don’t use the LP filter because I am pretty convinced that with light pollution it also removes some valuable data leaving the image dominated by blue and purple.
Perhaps on some other targets such as M45, where the nebulosity is almost entirely blue, the LP filter may help.
I’m going to try this on M45 when the weather improves ...