Astronomik SII 4nm Filter - 50mm Round Unmounted
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- SII Narrowband: Precisely isolates the sulfur-II emission lines (671.7 nm and 673 nm) for significantly boosted nebula contrast and detail.
- Light Pollution Suppression: The tighter 4 nm bandpass filters out unwanted skyglow and artificial light, improving signal-to-noise and making faint hydrogen-rich structures more visible.
- High-Quality Optics: Designed with Astronomik’s premium MFR coating and precision glass for sharp stars, excellent contrast, and minimal stray light or halos.
- Parfocal Performance: Works seamlessly with other Astronomik filters with no refocusing needed, preserving optical performance across channels for imaging setups.
Astronomik 4 nm Filter: Nebulosity like Never Before
Astronomiks continues to lengthen their impressive list of astrophotography filters with this narrow 4 nm sulfur (SII) 50 mm unmounted imaging filter! Ideal for nebulae, this filter will boost and contrast faint nebulosity from both light-polluted and dark observation sites. By allowing only certain SII emissions in, you will see a significant reduction of common pesky light pollution emissions like sodium (Na), mercury (Hg), and most natural moon/sky glow. The 4 nm suppresses more sky background and light pollution improving the signal-to-noise ratio—delivering cleaner subs, higher contrast, and the kind of fine SII detail narrowband imagers crave.
Spotlight Features:
-
Narrower 4 nm bandpass for finer nebulous details in each exposure.
-
Astronomiks MFR coating enhances contrast and reduces reflections or halos.
-
Finely polished optical glass, free of any striae, residual stresses, and bubbles.
-
Coatings resistant to scratching and humidity for a longer use life.
-
Parfocal with other Astronomik filters.
Targeted SII Emissions
This narrowband filter precisely isolates the SII emission line at 671.7 nm and 673 nm, cutting through light pollution and sky glow to deliver high-contrast views of sulfur-rich nebulae such as the Heart and Soul, North America, Veil, and Crescent Nebulae. The tight 4 nm bandwidth improves signal-to-noise, allowing faint structures in emission and planetary nebulae to stand out with striking clarity.
Tried and True MFR Coatings
The new 4 nm filters use Astronomik’s proven MFR coating, designed to deliver sharp stars, strong contrast, and clean images with minimal reflections or halos. This advanced coating also provides excellent blocking from UV to IR light, helping reduce unwanted background glow. One of the biggest advantages of the MFR coating is its versatility. Astronomik narrowband filters work reliably with nearly all telescope designs and focal ratios, so you don’t need different filters for fast or slow optics. Unlike many competing filters that require special “high-speed” versions, Astronomik’s MFR filters maintain consistent performance across a wide range of setups, making them a flexible and future-proof choice for imagers.
Picking the Best Bandpass for You
The choice between 12 nm, 6 nm and 4 nm Full-Width-Half-Maximum (FWHM) filters depends on your imaging conditions and camera. There is no universal “best” option—each filter serves a specific purpose.
- Wider 12 nm: Offers a broader window around the SII emission lines, making it easier to capture more stars and guiding reference points, and works well with typical DSLR/CMOS cameras and less aggressive light pollution conditions.
- Medium 6 nm: Tighter isolation of the SII wavelengths helps cut more sky glow and contrast against other background light while still letting enough signal through for many imaging setups.
- *New* Narrow 4 nm: Reduces background interference by about 70% compared to the 12 nm filters. This typically boosts contrast under strong light pollution and can help your target “pop” more against the sky background, though it may reduce overall signal and visible stars in the field—a trade-off many narrowband imagers will tolerate for finer nebulous detail.
Parfocal Performance
Each Astronomik filter is manufactured to extremely tight tolerances, making them fully parfocal and diffraction-limited. This means no focus shift between filters, precise image alignment across color channels, and no loss of resolution or contrast. Designed for both modern CMOS and CCD cameras, these filters deliver sharp, high-contrast images with no halos or reflections—capturing fine detail in nebulae and galaxies even when bright stars are in the frame.
Specifications
- Type: Sulfur (SII)
- Filter compatibility: 50 mm unmounted (protective ring provided filter wheels without screw thread)
- Glass thickness: 1 mm
- Diameter: 50 mm
- Coatings: Astronomiks MFR
- Transmission: Guaranteed more than 90% at the SII line (671.7 nm and 673 nm)
- Typical transmission: 93% at the SII line
- Parfocal: Yes, with other Astronomik filters
- Diffraction-limited
- Optimized spectral windows
Important note: Astronomik filters undergo a rigorous quality control process before delivery. Each narrowband-emission filter is measured using a high-end PerkinElmer Spectrophotometer to ensure it meets the specifications published on Astronomiks website. On the back of each narrowband filter box you will find a label detailing the precise spectral data for that specific filter. This includes the maximum transmission and the recommended range of focal ratios.
Other Information
- Country of Manufacture: Germany
Astronomik 4 nm Filter: Nebulosity like Never Before
Astronomiks continues to lengthen their impressive list of astrophotography filters with this narrow 4 nm sulfur (SII) 50 mm unmounted imaging filter! Ideal for nebulae, this filter will boost and contrast faint nebulosity from both light-polluted and dark observation sites. By allowing only certain SII emissions in, you will see a significant reduction of common pesky light pollution emissions like sodium (Na), mercury (Hg), and most natural moon/sky glow. The 4 nm suppresses more sky background and light pollution improving the signal-to-noise ratio—delivering cleaner subs, higher contrast, and the kind of fine SII detail narrowband imagers crave.
Spotlight Features:
-
Narrower 4 nm bandpass for finer nebulous details in each exposure.
-
Astronomiks MFR coating enhances contrast and reduces reflections or halos.
-
Finely polished optical glass, free of any striae, residual stresses, and bubbles.
-
Coatings resistant to scratching and humidity for a longer use life.
-
Parfocal with other Astronomik filters.
Targeted SII Emissions
This narrowband filter precisely isolates the SII emission line at 671.7 nm and 673 nm, cutting through light pollution and sky glow to deliver high-contrast views of sulfur-rich nebulae such as the Heart and Soul, North America, Veil, and Crescent Nebulae. The tight 4 nm bandwidth improves signal-to-noise, allowing faint structures in emission and planetary nebulae to stand out with striking clarity.
Tried and True MFR Coatings
The new 4 nm filters use Astronomik’s proven MFR coating, designed to deliver sharp stars, strong contrast, and clean images with minimal reflections or halos. This advanced coating also provides excellent blocking from UV to IR light, helping reduce unwanted background glow. One of the biggest advantages of the MFR coating is its versatility. Astronomik narrowband filters work reliably with nearly all telescope designs and focal ratios, so you don’t need different filters for fast or slow optics. Unlike many competing filters that require special “high-speed” versions, Astronomik’s MFR filters maintain consistent performance across a wide range of setups, making them a flexible and future-proof choice for imagers.
Picking the Best Bandpass for You
The choice between 12 nm, 6 nm and 4 nm Full-Width-Half-Maximum (FWHM) filters depends on your imaging conditions and camera. There is no universal “best” option—each filter serves a specific purpose.
- Wider 12 nm: Offers a broader window around the SII emission lines, making it easier to capture more stars and guiding reference points, and works well with typical DSLR/CMOS cameras and less aggressive light pollution conditions.
- Medium 6 nm: Tighter isolation of the SII wavelengths helps cut more sky glow and contrast against other background light while still letting enough signal through for many imaging setups.
- *New* Narrow 4 nm: Reduces background interference by about 70% compared to the 12 nm filters. This typically boosts contrast under strong light pollution and can help your target “pop” more against the sky background, though it may reduce overall signal and visible stars in the field—a trade-off many narrowband imagers will tolerate for finer nebulous detail.
Parfocal Performance
Each Astronomik filter is manufactured to extremely tight tolerances, making them fully parfocal and diffraction-limited. This means no focus shift between filters, precise image alignment across color channels, and no loss of resolution or contrast. Designed for both modern CMOS and CCD cameras, these filters deliver sharp, high-contrast images with no halos or reflections—capturing fine detail in nebulae and galaxies even when bright stars are in the frame.
Specifications
- Type: Sulfur (SII)
- Filter compatibility: 50 mm unmounted (protective ring provided filter wheels without screw thread)
- Glass thickness: 1 mm
- Diameter: 50 mm
- Coatings: Astronomiks MFR
- Transmission: Guaranteed more than 90% at the SII line (671.7 nm and 673 nm)
- Typical transmission: 93% at the SII line
- Parfocal: Yes, with other Astronomik filters
- Diffraction-limited
- Optimized spectral windows
Important note: Astronomik filters undergo a rigorous quality control process before delivery. Each narrowband-emission filter is measured using a high-end PerkinElmer Spectrophotometer to ensure it meets the specifications published on Astronomiks website. On the back of each narrowband filter box you will find a label detailing the precise spectral data for that specific filter. This includes the maximum transmission and the recommended range of focal ratios.
- 4nm SII 50 mm filter
- Protective ring
- High-quality filter storage case
- SII Narrowband: Precisely isolates the sulfur-II emission lines (671.7 nm and 673 nm) for significantly boosted nebula contrast and detail.
- Light Pollution Suppression: The tighter 4 nm bandpass filters out unwanted skyglow and artificial light, improving signal-to-noise and making faint hydrogen-rich structures more visible.
- High-Quality Optics: Designed with Astronomik’s premium MFR coating and precision glass for sharp stars, excellent contrast, and minimal stray light or halos.
- Parfocal Performance: Works seamlessly with other Astronomik filters with no refocusing needed, preserving optical performance across channels for imaging setups.
Astronomik 4 nm Filter: Nebulosity like Never Before
Astronomiks continues to lengthen their impressive list of astrophotography filters with this narrow 4 nm sulfur (SII) 50 mm unmounted imaging filter! Ideal for nebulae, this filter will boost and contrast faint nebulosity from both light-polluted and dark observation sites. By allowing only certain SII emissions in, you will see a significant reduction of common pesky light pollution emissions like sodium (Na), mercury (Hg), and most natural moon/sky glow. The 4 nm suppresses more sky background and light pollution improving the signal-to-noise ratio—delivering cleaner subs, higher contrast, and the kind of fine SII detail narrowband imagers crave.
Spotlight Features:
-
Narrower 4 nm bandpass for finer nebulous details in each exposure.
-
Astronomiks MFR coating enhances contrast and reduces reflections or halos.
-
Finely polished optical glass, free of any striae, residual stresses, and bubbles.
-
Coatings resistant to scratching and humidity for a longer use life.
-
Parfocal with other Astronomik filters.
Targeted SII Emissions
This narrowband filter precisely isolates the SII emission line at 671.7 nm and 673 nm, cutting through light pollution and sky glow to deliver high-contrast views of sulfur-rich nebulae such as the Heart and Soul, North America, Veil, and Crescent Nebulae. The tight 4 nm bandwidth improves signal-to-noise, allowing faint structures in emission and planetary nebulae to stand out with striking clarity.
Tried and True MFR Coatings
The new 4 nm filters use Astronomik’s proven MFR coating, designed to deliver sharp stars, strong contrast, and clean images with minimal reflections or halos. This advanced coating also provides excellent blocking from UV to IR light, helping reduce unwanted background glow. One of the biggest advantages of the MFR coating is its versatility. Astronomik narrowband filters work reliably with nearly all telescope designs and focal ratios, so you don’t need different filters for fast or slow optics. Unlike many competing filters that require special “high-speed” versions, Astronomik’s MFR filters maintain consistent performance across a wide range of setups, making them a flexible and future-proof choice for imagers.
Picking the Best Bandpass for You
The choice between 12 nm, 6 nm and 4 nm Full-Width-Half-Maximum (FWHM) filters depends on your imaging conditions and camera. There is no universal “best” option—each filter serves a specific purpose.
- Wider 12 nm: Offers a broader window around the SII emission lines, making it easier to capture more stars and guiding reference points, and works well with typical DSLR/CMOS cameras and less aggressive light pollution conditions.
- Medium 6 nm: Tighter isolation of the SII wavelengths helps cut more sky glow and contrast against other background light while still letting enough signal through for many imaging setups.
- *New* Narrow 4 nm: Reduces background interference by about 70% compared to the 12 nm filters. This typically boosts contrast under strong light pollution and can help your target “pop” more against the sky background, though it may reduce overall signal and visible stars in the field—a trade-off many narrowband imagers will tolerate for finer nebulous detail.
Parfocal Performance
Each Astronomik filter is manufactured to extremely tight tolerances, making them fully parfocal and diffraction-limited. This means no focus shift between filters, precise image alignment across color channels, and no loss of resolution or contrast. Designed for both modern CMOS and CCD cameras, these filters deliver sharp, high-contrast images with no halos or reflections—capturing fine detail in nebulae and galaxies even when bright stars are in the frame.
Specifications
- Type: Sulfur (SII)
- Filter compatibility: 50 mm unmounted (protective ring provided filter wheels without screw thread)
- Glass thickness: 1 mm
- Diameter: 50 mm
- Coatings: Astronomiks MFR
- Transmission: Guaranteed more than 90% at the SII line (671.7 nm and 673 nm)
- Typical transmission: 93% at the SII line
- Parfocal: Yes, with other Astronomik filters
- Diffraction-limited
- Optimized spectral windows
Important note: Astronomik filters undergo a rigorous quality control process before delivery. Each narrowband-emission filter is measured using a high-end PerkinElmer Spectrophotometer to ensure it meets the specifications published on Astronomiks website. On the back of each narrowband filter box you will find a label detailing the precise spectral data for that specific filter. This includes the maximum transmission and the recommended range of focal ratios.
Other Information
- Country of Manufacture: Germany
- 4nm SII 50 mm filter
- Protective ring
- High-quality filter storage case
Astronomik SII 4nm Filter - 50mm Round Unmounted