Planeoptically polished for the highest images quality. Produces a much brighter image with superb contrast than a conventional Nebula filter. Excellent for openings from 100mm.
A new class of LPR Nebula filters finally delivering the happy medium, with enough light for smaller telescope openings at the same time with the high contrast of classical UHC filter.
Light pollution from street lights is blocked carefully. The filter is the sensible addition to all previous deep sky and UHC filters. Both for visual as well as photographic use.
All filters produce a brighter image and are optically polished with ultra-hard dielectric coatings. They are absolutely scratch resistant and can be cleaned as often as needed, ideally with Baader Optical Wonder Cleaning Fluid.
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.