The Astronomik SII filter is ideal for imaging nebulae showing sulfur emissions from both light-polluted and dark observation sites. It significantly enhances the contrast between objects emitting light at 671.7nm and 673nm (SII lines) and the sky background. The Astronomik SII filter completely filters out the emission lines from high- and low-pressure sodium (Na)- and mercury (Hg)-vapor lamps, as well as all lines of natural airglow and most of the distracting moonlight.With a narrow bandwidth of either 12nm or 6nm and high transmission rates, the filter effectively blocks all unwanted light from wavelengths other than 671.7nm and 673nm from ultraviolet (UV) to infrared (IR).In areas with little light pollution, the background signal in images is usually limited by the sensor's dark current rather than light pollution. Therefore, further suppression of the sky background by reduction of the Full-Width-Half Maximum (FWHM) does not bring out more details in the object. Imaging with Astronomik Narrowband-Emissionline filtersImaging with Astronomik Narrowband-Emissionline filters is the best way to capture great images from light-polluted sites as they effectively block all kinds of light pollution. An Astronomik H-alpha filter is usually the first step in this field of astrophotography, allowing you to take deep and contrasty images even under heavy light pollution or a full moon. Astronomik H-alpha filters are ideal for imaging all red-glowing nebulae. Astronomik OIII filters expand your imaging possibilities by capturing greenish and blueish structures, making planetary nebulae, star-forming regions and supernova remnants great targets. Completing your filter set with an Astronomik SII filter enables you to create false-color emission line images similar to those produced by the Hubble Space Telescope using the HSO (H-alpha, SII, OIII) palette. Difference between Astronomik SII 12nm and 6nm filtersThe 6nm Astronomik Narrowband-Emissionline filters are ideal for imaging faint objects in star-crowded regions of the milky way, as they typically halve the number of stars in the image. They are also suitable if you have a camera with very low dark current or if you are observing from a location with extreme light pollution.The 12nm Astronomik Narrowband-Emissionline filters are better suited for use with typical DSLR cameras with CMOS sensors and CCD cameras with normal or high dark current. They are also the preferred choice for cameras with an integrated or dual guiding sensor, as they generally provide more guiding stars.Difference between Astronomik MFR and MaxFR coatingBoth the Astronomik MFR and MaxFR coatings give you the best out-of-band blocking over the entire wavelength range from UV to IR, extremely high contrast, minimized stray light, no halos and needle-sharp stars. 12nm MFR-coated filters can be used in all instruments with aperture ratios from f/3 to f/∞ without significant performance loss.6nm MFR-coated filters can be used in all instruments with aperture ratios from f/4 to f/∞ without significant performance loss.The MaxFR coating is designed to work perfectly with fast optical systems. For 12nm filters with MaxFR coating, this means unlimited usability from f/1.7 to f/8 and approximately 85% of the maximum transmission at a f/1.4.For 6nm filters with MaxFR coating, this means unlimited usability from f/2.2 to f/8 and approximately 90% of the maximum transmission at a f/2.Technical dataGuaranteed transmission of more than 90% (12nm and 6nm) at both SII lines (671.7nm and 673.0nm)Typical transmission of 96% (12nm) and 93% (6nm) at both SII lines Glass thickness: 1mm (except Astronomik OWB Type 3 and XT filters)Finely polished optical glass, free of any striae, residual stresses, and bubblesExtremely scratch-resistant and durable coatingCompletely resistant against high humidity and aging effectsAstronomik MFR coating (Astronomik Deep-Sky RGB, UV-IR Block L-1, L-2, L-3, and Narrowband-Emissionline filters)Parfocal with other Astronomik filtersDiffraction-limitedOptimized spectral windowsDelivered in a high-quality, long-lasting filter boxDue to the high-precision machining of the carrier substrate, all Astronomik filters are parfocal with wedge errors far below all common tolerances. Astronomik filters are diffraction-limited, ensuring that the optical performance (resolution and contrast) of your telescope is not compromised. Issues concerning focal distances and the exact alignment of images from each color channel are therefore effectively eliminated. All Astronomik filters are ideal for modern cameras, including both CMOS- and CCD-based models, ensuring you capture the best possible images with your equipment. Sharpness, contrast, and the absence of any reflections and halos are guaranteed. Even with bright stars in the field of view, nebulae and galaxies will be captured with the finest structures. The Astronomik MFR coating is designed for optimal performance across a wide range of focal ratios of the optics used.Every Astronomik filter undergoes a rigorous quality control process before delivery. Additionally, each Astronomik Narrowband-Emissionline filter is measured using a high-end PerkinElmer Spectrophotometer to ensure it meets the specifications published on our website. On the back of each Narrowband-Emissionline filter box, you will find a label detailing the precise spectral data for that specific filter, including the maximum transmission and the recommended range of focal ratios.

The Astronomik SII filter is ideal for imaging nebulae showing sulfur emissions from both light-polluted and dark observation sites. It significantly enhances the contrast between objects emitting light at 671.7nm and 673nm (SII lines) and the sky background. The Astronomik SII filter completely filters out the emission lines from high- and low-pressure sodium (Na)- and mercury (Hg)-vapor lamps, as well as all lines of natural airglow and most of the distracting moonlight.With a narrow bandwidth of either 12nm or 6nm and high transmission rates, the filter effectively blocks all unwanted light from wavelengths other than 671.7nm and 673nm from ultraviolet (UV) to infrared (IR).In areas with little light pollution, the background signal in images is usually limited by the sensor's dark current rather than light pollution. Therefore, further suppression of the sky background by reduction of the Full-Width-Half Maximum (FWHM) does not bring out more details in the object. Imaging with Astronomik Narrowband-Emissionline filtersImaging with Astronomik Narrowband-Emissionline filters is the best way to capture great images from light-polluted sites as they effectively block all kinds of light pollution. An Astronomik H-alpha filter is usually the first step in this field of astrophotography, allowing you to take deep and contrasty images even under heavy light pollution or a full moon. Astronomik H-alpha filters are ideal for imaging all red-glowing nebulae. Astronomik OIII filters expand your imaging possibilities by capturing greenish and blueish structures, making planetary nebulae, star-forming regions and supernova remnants great targets. Completing your filter set with an Astronomik SII filter enables you to create false-color emission line images similar to those produced by the Hubble Space Telescope using the HSO (H-alpha, SII, OIII) palette. Difference between Astronomik SII 12nm and 6nm filtersThe 6nm Astronomik Narrowband-Emissionline filters are ideal for imaging faint objects in star-crowded regions of the milky way, as they typically halve the number of stars in the image. They are also suitable if you have a camera with very low dark current or if you are observing from a location with extreme light pollution.The 12nm Astronomik Narrowband-Emissionline filters are better suited for use with typical DSLR cameras with CMOS sensors and CCD cameras with normal or high dark current. They are also the preferred choice for cameras with an integrated or dual guiding sensor, as they generally provide more guiding stars.Difference between Astronomik MFR and MaxFR coatingBoth the Astronomik MFR and MaxFR coatings give you the best out-of-band blocking over the entire wavelength range from UV to IR, extremely high contrast, minimized stray light, no halos and needle-sharp stars. 12nm MFR-coated filters can be used in all instruments with aperture ratios from f/3 to f/∞ without significant performance loss.6nm MFR-coated filters can be used in all instruments with aperture ratios from f/4 to f/∞ without significant performance loss.The MaxFR coating is designed to work perfectly with fast optical systems. For 12nm filters with MaxFR coating, this means unlimited usability from f/1.7 to f/8 and approximately 85% of the maximum transmission at a f/1.4.For 6nm filters with MaxFR coating, this means unlimited usability from f/2.2 to f/8 and approximately 90% of the maximum transmission at a f/2.Difference between Astronomik standard and XT Clip-FiltersThe new Astronomik XT-Filters are specifically designed for astrophotography with wide-angle lenses, delivering sharp and crisp star images all the way to the edges of the image. When using very short focal length lenses to take widefield images, standard Clip-Filters could introduce aberrations, stretching stars in the outermost corners of the image. To solve this issue, the new Astronomik XT-Filters are coated on an extremely thin substrate of only 0.3mm or 0,5mm thickness, significantly reducing these aberrations. Despite the reduced thickness, the Astronomik XT-Filters maintain the highest optical quality. They are manufactured using the same durable coating technology as all Astronomik filters. More information about our XT-Filters can be found here.Technical dataGuaranteed transmission of more than 90% (12nm and 6nm) at both SII lines (671.7nm and 673.0nm)Typical transmission of 96% (12nm) and 93% (6nm) at both SII lines Glass thickness: 1mm (except Astronomik OWB Type 3 and XT filters)Finely polished optical glass, free of any striae, residual stresses, and bubblesExtremely scratch-resistant and durable coatingCompletely resistant against high humidity and aging effectsAstronomik MFR coating (Astronomik Deep-Sky RGB, UV-IR Block L-1, L-2, L-3, and Narrowband-Emissionline filters)Parfocal with other Astronomik filtersDiffraction-limitedOptimized spectral windowsDelivered in a high-quality, long-lasting filter boxDue to the high-precision machining of the carrier substrate, all Astronomik filters are parfocal with wedge errors far below all common tolerances. Astronomik filters are diffraction-limited, ensuring that the optical performance (resolution and contrast) of your telescope is not compromised. Issues concerning focal distances and the exact alignment of images from each color channel are therefore effectively eliminated. All Astronomik filters are ideal for modern cameras, including both CMOS- and CCD-based models, ensuring you capture the best possible images with your equipment. Sharpness, contrast, and the absence of any reflections and halos are guaranteed. Even with bright stars in the field of view, nebulae and galaxies will be captured with the finest structures. The Astronomik MFR coating is designed for optimal performance across a wide range of focal ratios of the optics used.Every Astronomik filter undergoes a rigorous quality control process before delivery. Additionally, each Astronomik Narrowband-Emissionline filter is measured using a high-end PerkinElmer Spectrophotometer to ensure it meets the specifications published on our website. On the back of each Narrowband-Emissionline filter box, you will find a label detailing the precise spectral data for that specific filter, including the maximum transmission and the recommended range of focal ratios.