Filter · MSRP $199 Optolong SII 6.5nm 36mm Optolong · SII 6.5nm 36mm Key specifications Filter typeNarrowband PassbandSII 672 nm Bandwidth6.5 nm Filter size36mm About Improved-version 6.5 nm SII narrowband imaging filter centered on 672 nm; 36 mm diameter, 2.0 mm thick.