Filter · MSRP $255 Optolong OIII 6.5nm 2" Optolong · OIII 6.5nm 2" Key specifications Filter typeNarrowband PassbandOIII 500 nm Bandwidth6.5 nm Filter size2" MountedYes About Improved-version 6.5 nm OIII narrowband imaging filter centered on 500 nm; 2-inch mounted.