Celestron"s 1.25-inch, Oxygen III narrowband filter is a must for viewing nebulae. Oxygen III filters transmit wavelengths from the two doubly ionized oxygen lines but block virtually all others. That gives increased detail and improved contrast when viewing diffuse and planetary nebulae. You"ll get stunning views of the Veil, Ring, Dumbbell, Crescent and Orion nebulae, among other objects. Each 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 unnatural, colored halos surrounding bright stars common with OIII filters of less-sophisticated coating technology. The 1-1/4"" OIII narrowband filter isolates just the two doubly-ionized oxygen lines (496 and 501nm lines) emitted by planetary and emission nebulae, while blocking the rest of the overall spectrum of light. 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 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 O III filters of less sophisticated coating technology. * 1.25 inch format OIII Narrowband filter * Isolates just the doubly-ionized oxygen lines * Extreme contrast vs black sky background * Excellent for the Veil, Ring, Dumbbell, Crescent and Orion * Designed to block all visual spectrum rage 400-700 nm