Ok, these are all using the same Subs 18x5 Minute Ha M42, ZS66 @ F4.
This is a raw stack uncalibrated
(http://farm4.static.flickr.com/3263/3158862243_34284c2f77_b.jpg)
This is using reference darks, not dark scaled, you can see the black lines, this is because the reference darks are warmer and have a greater ADU reading.
(http://farm4.static.flickr.com/3077/3158862787_3a553f3b49_b.jpg)
Now with Reference Darks (scaled), Flats, Flat Darks & BIAS removed, average stack.
(http://farm4.static.flickr.com/3109/3158863337_4d3cfe1598_b.jpg)
Now the same as above but Sigma stacking is used.
(http://farm4.static.flickr.com/3262/3159697754_3ed8ff8b09_b.jpg)
Now I allways have thought and ADV stack is better than a SIG stack providing your calibration is right, from home that is mainly because the SIG stack seems to make the image a little noisier and also seems to remove some signal. See what you think?
All the images were brightness scaled the same way.