I have Baader SHO LRGB 36mm filters (iirc these are 6nm) from a while back when I purchased an ST-8300m.
I am now using the these filters with a QHY-268M.
I've been considering getting narrower SHO filters , e.g. 3nm.
(And, btw, I won't be using fast optical systems -- the fastest OTA I have is f5, tho I'm doing some experiments with a 12" at f4.)
It seems the word on the 'net is the Astrodon or Chroma filters are the ones to get, but they are pricey at about (?) $2.5k for the set (Chroma may be more $$).
(Also, availability seems to be problematic, as was the case years ago when I considered Astrodon instead of Baader.)
Now, I see Baader has these "CMOS" optimized filters, and the message is lots of work/testing was done to reduce/eliminate Halos.
Fwiw, I do have some bright star halo issues with the current filters... and thinking about it, I'm thinking the halos are specific to using a flattner (and possibly a reducer).
(I'll need to do some experiments, but I don't think I get Halos with some OTAs where I don't use a flattner or reducer.)
Also, regarding the Halos and "CMOS": I had halos with the ST-8300m camera, so it's not CMOS specific.
Anyhow, the new Baader 3nm filters are "reasonably" priced (afaict) (not sure about availability tho), and I'm considering taking the plunge.
Anything else out there I'm missing that I should consider?
Ps here's an M17 HOO with Baader filters and QHY268M, 6x5min on Ha and OIII each, and it could use better processing.