I forgot to say that the NII thingy image at 10x8 minutes or 80 minutes total is equivalent to 10x22 minutes or 220 minutes total with an optic at F5 with the same focal length. At f10 88 minute exposures would be needed to get close. With about a third the exposure the time dependant noise associated with any CCD is also cut to a third which further enhances the signal to noise.
This is the whole point of this system. With the very fast optics it is now practical to image very dim stuff with 3nm NB filters. It is not surprising that magnitude 1 stars in or near the image field will be a problem.
Contrary to popular belief a 3nm NB filter does not attenuate a fast wide field.
See here
http://www.astrodon.com/Orphan/astro...arrowband/#h10
Below is a screen grab of a NII flat with a line profile. This flat was taken before the system was aligned and held by the wood frame hence the slight assymetry.
Bert