Yeah, this is a tough one. The gas filter and band pass stats are nice and all, but the fact remains that many of us are stuck with our driveway or backyard most nights - particularly when one wants to grab-and-go for an hour or two before having to work the next day.
I am in a brutal red zone with Bortle 6-7 skies most nights. Yet, I've been able to capture most of the mag 10.5 and brighter Messiers and NCGs. Some filters I have found work rather well in an urban/suburban environment:
1. The Elevation Filter - Higher is better, and the closer to zenith, the more you'll see. Aim high - ideally above 45 degrees for best results. M51 is invisible from my skies, but when it is straight overhead, it's obvious.
2. The Transparency Filter - A seemingly clear night clear night isn't necessarily a clear night - particularly for galaxies. Real transparency is vital, as slight haze, dust, or humidity all reflect urban light and can drown out faint fuzzies on otherwise clear nights. Couldn't see a darn thing last night, even though it seemed to be clear as a bell!
3. The Take-a-nap-and-go-out-later Filter - I can always see more galaxies viewing from 1-4 am, after more city lights are turned off after midnight. One night last week from 10-11:30pm, it was hopeless. Got up later and from 3-5 am, and bagged more than 30 spring Messier and NCG galaxies in a single session. Take a nap, set your alarm, and go out later.
4. The Magnification Filter - Find it (or where you know it is), and then crank up the power to 150x or 200x. It might peek out a bit due to the darker sky background and smaller exit pupil.
5. The Old Fashioned Skinny Eyepiece Filter - Sometimes, a narrower FOV eyepiece is better once you find the galaxy. A 45-55-degree field focuses your eye and perception a bit more when you are trying to tease a smudge out of urban gray.
4. The "Gentle" Filter - Yes, some filters do help a TINY bit, despite the naysayers. Moon & Skyglows (particularly the Baader) and more gentle broadbands like the Lumicon Deep Sky don't have much effect and they do darken the galaxy as well. However sometimes, as you have experienced, they darken the background enough that your eye can sense the object a bit more. If it works for you, do it.
Don't expect what you can see from dark skies, but keep at it. You'll find that over time, you can tease out most of the mid-to-bright ones visible with diligence and practice. It's all the more rewarding when you actually see them, despite the urban fog.
Edited by PJBilotta, 06 April 2021 - 10:04 PM.