The Orion 20mm Sirius Plossl Eyepiece offeres a wide 52° apparent field of view which provides extremely sharp images of impressively high contrast. It's ideal for all types of telescopes: reflector, refractor and catadioptric. The Plossl 4-element design is renowned for its outstanding performance and has become the standard by which all other eyepieces are judged. The Sirius Plossl optical system is fully coated with magnesium fluoride on every air-to-glass surface. Lens edges are blackened to reduce scattering of stray light and maximize contrast.
The lenses are mounted in black-anodized aluminum housings with a 1.25"-diameter chrome-plated brass barrel for durability and precision fit. The barrel is internally threaded to accept standard filters. The built-in rubber eyeguard enhances viewing by helping to block out ambient light and position the eye. This 20mm eyepiece excels for moderately low power scanning of open star clusters and viewing of extended nebulas and larger galaxies.