The Baader 6.5nm Narrowband-Filter-Set 2" CMOS-optimized (H-alpha / O-III / S-II) is a precision grade filter with 2" (M48) filter thread. 6.5 nm FWHM, recommended for optical systems from f/10 to f/3.5. This filter has reflex-Blockerô hard coated and planeoptically polished with sealed coating edges (Life-Coatô). Blackened edges all around, with filter-lead-side-indicator in the form of a telescope-sided black outer rim Optimized for modern CMOS cameras, but likewise excellent for CCD camera technologies. Mounted in Baader Low Profile Filter Cell (LPFC) Ė 6 mm height.