Celestron Oxygen-III Narrowband Filter - 2in. The result is extreme contrast between the black sky background and the faint photons of OIII light needed for detailed views of the Veil Ring Dumbbell Crescent and Orion nebulae among other objects. Each Celestron OIII Filter has an ultra hard vacuum-deposited coating carefully designed to block all of the visual spectrum ranging from 400 to 700 nm. This eliminates the un-natural colored halos surrounding bright stars common with Celestron O III Narrowband Filters of less sophisticated coating technology. There are Celestron Oxygen III Narrowband Filter 1.25" (model 93623) and Celestron Oxygen-III Narrowband Fulter 2" (model 93624). Features of Celestron OIII Filters: Narrowband filter for high transmission and high-contrast images Blocks unwanted light-pollution Ideal for viewing planetary nebulae and supernova remnants Package Contents: Clestron Oxygen III Narrowband Filter