H-alpha filter passes light at 656nm wavelength. Best choice of narrowband H-alpha astrophotography filter for high-contrast imaging and revealing rich details of the nebula even in areas with strong light pollution,
H-Alpha 7 nm filter is the most popular narrowband filter allowing 7 nm bandwidth of light centered on a wavelength of 656 nm through, and reducing the transmission of certain wavelengths of light, specifically those produced by artificial light including mercury vapor, and both high and low pressure sodium vapor lights and the unwanted natural light caused by neutral oxygen emission in our atmosphere (skyglow).
