Chroma SII 3nm Ultra filter - 2″ mounted

SII 3nm filter from Chroma Technology

Visit 3nm SII filter from Chroma Technology is an ultra-narrow band filter designed to isolate the emission line of ionized sulfur (SII) at 672 nm. This filter is particularly suited to imaging nebulae, where sulfur plays a key role in spectral emission. It is ideal for astrophotographers seeking maximum contrast and clear separation of the different spectral lines.

Key features

• Bandwidth : 3 nm, enabling extremely precise isolation of the SII line, while effectively blocking unwanted wavelengths (light pollution, H-alpha, etc.).
• Targeted emission rays : SII doublet at 671.6 nm and 673.1 nm, characteristic of sulfur-rich nebulae.
• High transmission : Up to 90 % at 672 nm, guaranteeing an excellent signal-to-noise ratio.
• Optical quality : Surface polished to an accuracy of λ/4.
• Multi-layer anti-reflective coatings : On both sides to minimize halos and stray reflections.
• Substrate thickness : Approx. 3 mm ± 0.05 mm, made from a unique optical glass substrate for exceptional durability.
• Parallelism : <30 arcsec, guaranteeing optimum image quality.

Applications

• Imaging SII-rich nebulae:
  • Perfect for capturing objects such as the Crab Nebula, Rosette Nebula and Veil Nebula.
• Reducing light pollution :
  • Effectively blocks unwanted wavelengths, even in urban or suburban environments.
• Advanced astrophotography :
  • Ideal complement to H-alpha and OIII filters for creating images in scientific palettes (SHO or Hubble palette).
• Compatibility with high-speed systems :
  • Works perfectly with focal ratios up to f/4.0.
  • An optimized version is available for high-speed systems (f/2.8 to f/3.6), to compensate for blueshift.

Technical highlights

• Exceptional durability :
  • Sputter coatings guarantee long-term spectral stability.
  • Resistant to extreme variations in temperature and humidity.
• Anti-halos design : Anti-reflective coatings eliminate halos around bright stars, delivering sharp, detailed images.
• Universal compatibility : Compatible with most filter wheels and drawers on the market.

Available formats

• Mounted : 1,25", 2"
• Unmounted : Customized formats (31 mm, 36 mm).

Conclusion

The filter Chroma SII 3nm is an essential tool for astrophotographers seeking to capture the subtle details of nebulae rich in ionized sulfur. Its optical precision, high transmission and ability to effectively reduce light pollution make it an essential choice for deep-sky imaging.