Filter · MSRP $250 Optolong SII 6.5nm 2" Optolong · SII 6.5nm 2" Key specifications Filter typeNarrowband PassbandSII 672 nm Bandwidth6.5 nm Filter size2" MountedYes About Improved-version 6.5 nm SII narrowband imaging filter centered on 672 nm; 2-inch mounted.