Lumicon's Night Sky Hydrogen-Alpha Filters are long-pass filters with a 50% transition from blocking to passing at about 640nm. At wavelengths longer than 650nm, transmittance is 90% or above. The filter is used as an extreme anti light-pollution filter, and for contrast-enhancement of emission nebulae and other astronomical objects bright in the infrared.
The LF3090, 2" Night Sky Hydrogen-Alpha Filter, threads into the nose-piece of industry-standard 2" Digital Imagers.
Manufacturer part number: LF3090