Start with the imaging conditions
For urban nebula imaging, check sky brightness, moon phase, and camera type before choosing a filter. A filter will not fix every problem, but the right match can make the first session much more predictable.
Dual-band filters fit color cameras
For one-shot color cameras, a dual-band filter that passes H-alpha and OIII is usually the easiest starting point. It raises emission-nebula contrast and helps control bright sky background during longer exposures.
Galaxies and reflection nebulae are different
Galaxies and reflection nebulae emit broadband light. Strong narrowband filters can remove too much signal, so planning around darker skies and moon distance matters more than aggressive light-pollution rejection.
Check before buying
- Filter size versus sensor size
- Band shift risk with fast optics
- Whether your target is emission-line or broadband
The most useful first filter is the one that matches your actual targets and observing site.