OPTOLONG NIKON FULL FRAME FILTER - UHC FILTER
UHC (Ultra High Contrast) is a light pollution filter for use in severely light polluted urban area. It selectively enhances emission from nebulas and suppresses the transmission of light pollution sources. UHC enhances the transmission of nebulas emissions and reduce background brightness mostly dominated by light pollution. It has narrower passband than CLS (City Light Suppression) and thus it is the better choice of imaging under severely light polluted areas due to its more rigorous light pollution suppression. Its wider passband towards the red end of the visible spectrum makes it exceptionally suitable for hydrogen emission dominated objects such as M42 Great Orion Nebula.
UHC selectively cuts out light pollution emission. For example, mercury vapor lamps, high and low pressure sodium vapor lights and skyglow caused by emission from neutral oxygen in our atmosphere. Among the emission lines enhanced are OIII (496, 500nm), H-beta (486nm), NII (654, 658nm), H-alpha (656nm) and SII (672nm).