Recent experiments with the ASI1600MM-C camera have highlighted it's flexibility, and fast narrowband imaging is a possiblity (provided you accept the limitations in well depth that this involves).
As an example, I shot some narrowband Ha (15), Oiii (25), and Sii (28) subs of the Helix last night, all 90 second subs with the camera set to a Gain of 200 and Offset of 28. So for a combined time of 102 minutes of data I have produced this image. Sure it is a bit grainy on the edges if you look at the full screen version on Astrobin, but I am not involved in calendar or imaging comps, and lets face it for most of us this is done for our personal enjoyment and sharing with family and friends (most of whom will never notice the quality difference anyway).
So here are the links to the Astrobin details page and the full screen version (where you can see some grainy areas).
http://www.astrobin.com/262936/
http://www.astrobin.com/full/262936/0/
I am not suggesting this would work everywhere, the Helix is in a dark nebula area. I will go back at some point and shoot this again at the much 'smoother' lower gain settings. But if you have limited time, it's an option.
