Oxygen III Narrowband Filter - 2"The 2" OIII narrowband filter isolates the two doubly ionized oxygen lines (496 and 501 nm lines) Filter has ultra hard, vacuum deposited coating Eliminates un natural colored halos surrounding bright stars The 2" OIII narrowband filter isolates just the two doubly ionized oxygen lines (496 and 501 nm lines) emitted by planetary and emission nebulae, while blocking the rest of the overall spectrum of light. The result is extreme contrast between the