Filter Optolong SII 6.5nm 50x50mm Optolong · SII 6.5nm 50x50mm 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; 50 x 50 mm square, 3.0 mm thick.