I am trying to work out the best filter to use for Photography under light polluted skies. The biggest problem I have are the sodium lights which give off an orange glow. This seems to be the main problem I have. I am trying to reduce the effects of the pollution and need a filter to do it. Can someone recommend a good 2" filter that would work well in this situation?
You need to know the emission spectrum of the street lights. Low pressure sodium lighting is dominated (but is not exclusively) by sodium lines, something like 590nm I think. Then you need a filter that blocks that part of the spectrum. However, you'd want to check that the 590nm part of the spectrum isn't important for your photographic objects.