The narrowband oxygen III filter yields high transmissivity through blocking unwanted longer wavelengths of light that aren't involved in your attempts to observe, giving higher contrast to your observing and photographic experiences. By isolating solely the two doubly-ionized oxygen lines(496 & 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 amongst other objects. Each filter has an ultra hard, vacuum-deposited coating carefully designed to block all of the visual spectrum ranging from 400-700nm, eliminating the unnatural colored halos surrounding bright stars common with less sophisticated O III filters.
