|
Objects with full (wide) spectra are not helped by nebula filters. Only nebulae are helped a lot by this type of filter.
There are a few choices for visual observing:
UHC filter (transmits the H-Beta and O-III lines in the nebular spectra)
H-Beta filter (transmits only the H-B line)
O-III filter (transmits only the O-III lines)
The best contrast will be with the narrowest filter that lets through the light you want to examine. Filters with wider bandwidths pass more light of the stars, but have less contrast on the nebulae.
As a general rule, O-III filters seem to work best on planetary nebulae, while the UHC filters seem to work best on bright emission nebulae. The H-Beta filter enhances a small number of objects in the sky the best (e.g.Horsehead, California nebula, etc).
The problem with generalities is that there are usually exceptions, and that is the case here, too.
But if I were to recommend the order to get them it would be UHC first, O-III second, and H-Beta last.
Broadband filters notch out a few of the artificial light sources, but have little effect on diminishing light pollution. I think their best use is in an already dark sky just to tune up the contrast a tiny bit.
Unfortunately, there is really only one effective light pollution filter--gasoline. You put it in your car and drive your scope to darker skies.
|