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25nm is almost as wide as the Lumicon UHC (26nm, used to be 24nm). The Lumicon H-Beta is 9nm. (Not even sure Lumicon has a h-beta anymore since being purchased by another firm).
Note the Horsehead requires dark skies first and then a large exit pupil (ideally 4-7mm). Once you have this a H-beta filter improves contrast further for the Horsehead to show. It is basically black on slightly less black. If you don’t meet the first two parameters then even a quality H-beta filter will struggle especially in suburban lighting.
I have seen the Horsehead in a 6” f5.5 Newtonian with Lumicon H-beta under very dark skies using 25mm Clave Plossl. I have not yet seen the Horsehead in suburban/city lighting.
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