In areas plagued with significant light pollution, our UltraBlock eyepiece filter greatly increases contrast of emission and planetary nebulas Allows you to see features and details through a telescope that would normally be lost due to light pollution Blocks all forms of light pollution while passing critical hydrogen-beta and ionized oxygen wavelengths of light Enhances the sky presence of a significant number of fainter deep-sky objects Use with any filter-thread equipped 1.25" Orion eyepiece. Metal filter cell construction. The UltraBlock is a great 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. From the Manufacturer In areas plagued with significant light pollution, our UltraBlock eyepiece filter greatly increases contrast of emission and planetary nebulas. Allows you to see features and details through a telescope that would normally be lost due to light pollution. Blocks all forms of light pollution while passing critical hydrogen-beta and ionized oxygen wavelengths of light. Enhances the sky presence of a significant number of fainter deep-sky objects. Use with any 1.25" Orion eyepiece threaded for filters