The Optolong SII 6.5nm CCD Filter (2″) is an extra-narrowband filter designed to isolate the sulfur-II (SII) emission line at 672nm, making it an essential tool for imaging emission nebulae from light-polluted skies. With a precise 6.5nm bandwidth and >80% transmission at the SII line, this filter delivers exceptional contrast and minimal star bloat, revealing delicate structures in deep-sky objects.

Ideal for advanced astrophotographers using monochrome cameras, the SII filter complements H-Alpha and OIII filters to construct high-resolution SHO (Hubble palette) narrowband images. Its ultra-thin metal cell houses precision-polished Schott B260 glass and is finished with a multi-layer anti-reflective coating using ion-assisted deposition technology.

From faint signal enhancement to dramatic background suppression, this 2″ SII filter enables imaging in conditions where broadband filters would strugglebringing rich sulfur detail to light with scientific precision.

• Filter Type: Extra Narrowband SII
• Center Wavelength: 672nm
• Bandwidth (FWHM): 6.5nm
• Transmission at SII Line: 80%
• Infrared Block: 7001100nm (built-in)
• Off-band Rejection: <0.1% at Hg (435nm, 578nm), Na (589nm)
• Filter Size: 2″ (50.8mm)
• Clear