Product DescriptionThe 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.Amazon.comThe Celestron 93623 Narrowband Oxygen III 1.25-inch filter is a remarkable advance for the serious visual observer of emission nebulae. One of the biggest advantages of narrowband filters is that by passing only the light emitted by nebulae, light from artificial sources like street lights is blocked. This allows you to take detailed exposures of nebulas from a suburban location that can rival shots from much darker sites. The Celestron 93623 is made of high quality, solid plane parallel glass.