Orion UltraBlock 2" light pollution filter

Dramatically Improves Views of Emission and Planetary Nebulas. The UltraBlock is the filter for deep-sky observers located at highly light-polluted sites. Blocks all forms of light pollution - mercury vapor and sodium emission bands - while passing the critical hydrogen-beta and ionized oxygen wavelengths. With an UltraBlock, emission and planetary nebulas "surface" from the washed out background sky. In dark skies, the UltraBlock also enhances the sky presence of a significant number of fainter deep-sky objects over unfiltered and wideband-filtered views. Available in 1.25" and 2".