Astronomik UHC professional deepsky filter (31.7mm)

You will enjoy using your Astronomik UHC filter because you will see more stars and more details in deep-sky-objects compared to using filters from all other manufacturers.

The Astronomik UHC (Ultra High Contrast) filter allows the transmission of nearly 100% of the radiation from both O-III and the H beta lines. Though the second window for the H-alpha-line is not intended for visual observing, it is important, if the filter is used with an electronic device. All annoying, scattered light from other wavelength sources, including local artificial light pollution, is reliably filtered out. With this strong blocking of the sky background an unexpected wealth of detail becomes visible for gas nebulae and planetary nebulae.

Main use

Astronomik UHC filters’ astounding high light transmission brings better views of deep-sky-objects even to small telescopes! The high transmission of our optical glass filters means that enough light is available to allow successful visual observations with telescopes beginning at 2" (50mm) aperture. Our Astronomik filters are optimized for use with telescope focal length f / ratios of f/4 to f/15. Transmission losses and chromatic distortions, which arise with other filters, only occur with Astronomik filters when extremely bright aperture ratios of 1:2 and more come into play. Another major advantage of our Astronomik UHC filter is the high optical quality of the filter glass. When using Astronomik UHC filters you will quickly notice the same needle-sharp stars which you are familiar with from your astronomical instrument without any filter!

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.