Optolong SII CCD 6.5nm 1.25" Mounted Filter

The Optolong SII CCD 6.5nm Filter (1.25") is engineered for serious narrowband astrophotography, capturing the faint sulfur-II emission line at 672nm with outstanding contrast and detail. With a precisely defined 6.5nm bandwidth, this filter significantly suppresses unwanted light pollution and skyglow, allowing sulfur-rich nebula structures to emerge even from suburban or city skies.

When paired with H-Alpha and OIII filters, the SII 6.5nm creates stunning tri-color (SHO) compositions modeled after Hubble Space Telescope imaging. The narrow bandwidth reduces star bloat and dramatically enhances structural contrast in deep-sky targets such as emission nebulae, planetary nebulae, and supernova remnants.

Built from Schott B260 optical glass and enhanced with Optolong’s advanced ion-assisted deposition coatings, the filter ensures minimal scatter, excellent durability, and long-term central wavelength stability. The ultra-thin CNC-machined filter cell features a 26mm clear aperture and is designed for high precision and mechanical integrity.

• Filter Type: Narrowband – SII (Sulfur-II)
• Center Wavelength: 672nm
• Bandwidth (FWHM): 6.5nm
• Transmission: ~80% at 672nm
• Infrared Block: 700–1100nm
• Off-band Rejection: <0.1% at Hg (435nm, 578nm), Na (589nm)
• Filter Size: 1.25" (31.75mm)
• Clear Aperture: 26mm
• Substrate: Schott B260 Optical Glass
• Glass Thickness: 2.0mm
• Surface Quality: 60/40 (MIL-O-13830)
• Wavefront Accuracy: λ/4
• Parallelism: <30 arcseconds
• Coating Method: Electron-Beam Evaporation with Ion-Assisted Deposition
• Filter Cell: CNC-Machined, Sandblasted, Black Anodized Aluminum
• Manufacturing System: Optolong Planetary Rotation Coating
• Certifications: RoHS, TUV Rheinland, Bureau Veritas

• Optolong 1.25" SII CCD 6.5nm Filter
• Protective Filter Case with High-Pressure EVA Foam