While chasing up several H alpha filters I came across this site (
http://www.nexstarsite.com/Reviews/B...ingeKiller.htm) about filters and this very curious statement that does make sense.
"One last note on the uniqueness of this filter. Baader suggests that the Fringe-Killer combined with their Red filter is perhaps the best Hydrogen-Alpha filter commercially available. This combination has a 95% transmission rate at the H-Alpha wavelength and yet costs very little. H-Alpha filters are great for imaging emission nebula in great detail, though a smaller pass-band would produce better results."
Theoretically I and many other people bought an achro scope, then a violet suppression filter and have some coloured filters for other tasks. I thought that I would combine my sirius optics violet and red filters and see how this goes with my CCD camera. It may be a cheap way to broad band H alpha imaging?