I felt all scientific this morning so I decided to see if an Ha filter
would work properly with Centaurus A, NGC 5128, given
that it has a red shift - would that put it outside the
band pass of a narrowband filter?
http://simbad.u-strasbg.fr/simbad/si...=SIMBAD+search
V(km/s) 547 z(~) 0.001826
Ha wavelength is = 656.281 nm
Ha = 656.281nm * 0.001826 = 1.1983691 nm
So the Ha emission line is shifted to the Red by 1.19nm = 657.48 nm
That's only a tiny amount.
Mathew has used a Chroma H-alpha 5nm Bandpass filter
so the 1.19 nm red shift is OK - well inside.
It's interesting though to see what an Astrodon 3nm filter would have done?
https://astronomyplus.com/product/as...-alpha-filter/
It's right on the edge at 80% pass so
20% of the light would have been lost!
cheers
Allan