This filter is designed to enhance the contrast of deep-sky objects and soften the brightness of the background sky, thanks to a sophisticated transmission that lets through light from the lines on which deep-sky objects shine (H-alpha, O -III , N-II, H-Beta, S-II…), but blocks harmful light emissions (for example the Hg line, or wavelengths of sodium vapor illumination). It also reduces background glow caused by oxygen in the atmosphere ("skyglow"). This filter is recommended for use in areas with light pollution and is suitable for both visual and photographic use.
Compared to other filters to reduce the effects of light pollution, such as UHC or CLS filters, this is a multi-bandpass filter that only minimally affects color rendering. Therefore, it is suitable for photographing objects that emit continuous light: not only emission nebulae, but also galaxies, star clusters, reflection nebulae, etc. You can achieve exposures up to 3 times longer than unfiltered exposures.
The treatments are not cemented onto the optical support, but are spread by electron beam evaporation and subsequent ion beam assisted deposition (IBAD process). This special process allows for extreme durability and scratch resistance, ensures central wavelength (CWL) stability, and prevents thermal drift. In addition, it allows a high transmission in the pass band and a high optical density in the range of blocked frequencies.
Attention, this filter must never be used only to observe the Sun!
|Coating of optical system||multiple|
Area of application
|Useful for photographs||yes|
|Nebulae & galaxies||yes|