Astronomik UHC deepsky filter (2")

The UHC filters are general purpose deepsky filters which blocks the light from Hg and Na lamps, but transmits all of important wavelengths, such as H-alpha, H-beta and O-III. UHC filters are available from many different manufacturers, checking the image below might help to choose the right one. As it is evident there is no such thing as UHC "standard". All of the filters transmits most of the light around H-alpha (656nm), Oxigen-III (501nm) and H-beta (485) lines. 

There are wider and narrower filters. But what might be the difference between them in practice? It depends on heavily the selected targets.

A general rule is that the narrowed the transmission is the higher the contrast is, meaning that they work excellently for emission, planetary nebulae and supernova remnants. They don't work that well on objects with wider spectrum, like stellar clusters, galaxies, open- and globular clusters. To photograph these a wider transmission, light pollution reduction filters are recommended.

So: for emission and planetary nebulae, and supernova remnant use a narrowband filter, like Astronomik or Castell UHC.