NPB – NARROW PASS BAND NEBULA FILTER
An ultra high contrast type of filter that is very effective for small and fainter emission planetary nebula, as well as a variety of bright nebula.
The NPB filter is characterized by its slightly narrower passband in the OIII and H-Beta emission lines – compared to for instance the Lumicon UHC – as well as by its inclusion of a secondary H-Alpha passband. The H-Alpha passband allows for the perception of faint red colors in nebulas that have strong emission in the H-alpha line (e.g. M42 and M8), especially when observing with larger telescopes.