Filter · MSRP $193 Optolong SII 6.5nm 31mm Optolong · SII 6.5nm 31mm Key specifications Filter typeNarrowband PassbandSII 672 nm Bandwidth6.5 nm Filter sizeOther About Improved-version 6.5 nm SII narrowband imaging filter centered on 672 nm; 31 mm diameter, 2.0 mm thick.