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Please note: This text was taken directly from the manufacturer.
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.
