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[QUOTE=N1;1331231]It does help with light pollution. As does a UHC. No big difference between them TBH.
The OIII filter has a double transmission window at 496 and 501nm. It's only useful for high excitation objects such as supernova remnants and planetary nebulae. Nothing else shines brightly at these wavelengths. You simply can't use an OIII filter as a general light pollution filter - it's far too restrictive. Anything emitting continuum will simply be dimmed - quite massively. The NAN is not a high excitation object, so it doesn't glow strongly at these wavelengths - you'll be cutting out far more light than you're letting through.
A more effective filter for objects like the NAN is a H-beta filter, which has a transmission window at 486nm. Again, that only works for specific objects - those glowing brightly in H-beta, and would not be an effective LP filter.
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