Thanks all.
Martin. The main thing I found, thanks to Atmos, is to get the colour balance right early in processing. And he put up a really good workflow
http://www.iceinspace.com.au/forum/s...d.php?t=184904
Ryan. I think you can get this sort of image with any of the faux-narrowband filters. While I think it's a bit better than the duo, I haven't compared it on the same object. I started on the helix though and found I need double the sub exposure to the same amount of photons compared to the duo - so it is definitely more selective