One thing I often read about narrowband filters is that they work best in dark skies and not so well where there is light polution.
The reason I think for this is that the filters are like a mirror reflecting back all light wavelengths except the ones they are designed to pass.
Under light poluted skies, the light that enters the eyelens of the eyepiece gets reflected straight back at you. I find if I observe in galaxy hunt mode with my top pulled over my head and around the focuser to block out stray light, it works ok
