Filter · 2021– Optolong OIII 3nm 36mm Optolong · OIII 3nm 36mm Key specifications Filter typeNarrowband PassbandOIII 500 nm Bandwidth3 nm Filter size36mm MountedNo About 3 nm OIII narrowband imaging filter centered on 500 nm, part of the SHO-3nm kit; 36 mm unmounted.