This 1.25" H-Beta line filter has a very narrow 15 Ångstrom passband centered on the nebula emission line of hydrogen-beta at 4865Å. This very narrow passband completely blocks the rest of the visual spectrum, including light pollution, natural airglow in Earth’s skies, etc. The result is an extreme contrast between the black background of space and the delicately attenuated H-Beta light (about one-third the brightness of H-Alpha emissions) needed to view a select few extremely faint objects such as the Horsehead, Cocoon, and California Nebulas