Chroma SII filter 5nm - 2″ mounted

5nm SII filter from Chroma Technology

Visit 5nm SII filter from Chroma Technology is a narrow-band filter designed for astronomical imaging. It is optimized to capture the ionized sulfur emission line (SII) at 672 nm, an essential spectral line for the study of planetary and diffuse nebulae. This filter is particularly suited to astrophotographers looking for high contrast and clear separation of different spectral lines.

Key features

• Bandwidth : 5 nm, enabling precise isolation of the SII line while blocking unwanted wavelengths such as H-alpha (656.3 nm).
• 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, guaranteeing exceptional durability.
• Parallelism : <30 arcsec, ensuring optimum image quality.

Applications

• Imaging SII-rich nebulae:
  • Ideal for capturing objects such as the Crab Nebula, Rosette Nebula and Veil Nebula.
• Reducing light pollution :
  • Effectively blocks unwanted wavelengths (sodium or mercury lamps), 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 may be required for very fast systems (f/2.8 to f/3.6) to compensate for the 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 5nm is an essential tool for deep-sky imaging. Its optical precision, high transmission and ability to efficiently isolate the spectral lines of ionized sulfur make it an essential choice for capturing the subtle details of SII-rich nebulae.