Celestron 48mm Oxygen III Line Band Filter for 2" Eyepieces

This new Celestron 2" Oxygen III light pollution line filter isolates the two glowing emission lines of doubly-ionized oxygen (at 4959 Ångstroms and 5007 Ångstroms) that are emitted by planetary and emission nebulas, while blocking the rest of the overall spectrum of light. The result is an extremely high contrast between the black sky background and the faint photons of glowing ionized oxygen.

It yields detailed views of the billowing tapestry of the Veil, Ring, Crescent, and Orion nebulas, among others. Its very narrow passband gives two to three times the contrast of a narrowband filter for observing brighter nebulas like M17 (the Swan) and M27 (the Dumbbell) from heavily light-polluted city locations. It is excellent for visually observing very faint planetary and gaseous nebulas (such as M76, the Little Dumbbell, and Barnard's Loop in Orion) that are normally invisible without a filter from mildly to moderately light-polluted sites. It is not designed for astrophotography or for observing reflection nebulas.

The filter has an ultra-hard vacuum-deposited multilayer dielectric coating that has been carefully designed to block all of the visual spectrum ranging from 400 to 700 nm, except for the narrow Oxygen III passband. This eliminates the unnatural colored halos surrounding bright stars that are often common with O III filters with less sophisticated coating technology. Ion beam hardened coatings provide excellent durability and resistance to scratching.

Comes in a protective clear plastic case. A ribbed rim makes it easy to thread in and remove the filter from an eyepiece in cold weather when wearing gloves.