Astronomik 6 nm SII MFR Narrowband Filter - 50 mm Round Unmounted

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Astronomik 6 nm SII MFR Narrowband Filter - 50 mm Round Unmounted
Item # AK-SII6-50R
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  • An Astronomik 6 nm MFR Narrowband SII Filter, together with the 6 nm OIII & H-alpha filters, are the perfect choice for false color imaging of emission nebulae.
  • The Astronomik 6 nm SII CCD Filter lets the 672 nm wavelength through and blocks everything else, including light pollution!
  • This 50 mm SII CCD filter is round and unmounted.
  • 6nm is an extremely narrowband filter and is best for cameras with low dark current, those who wish to separate a faint object from an overly populated background of stars, or those imaging from severely light polluted skies.
  • The specially formulated Multi-Focal Ratio coatings applied to Astronomik 6 nm MFR Emissionline filters means you can use them with telescopes as fast as f/4 without bandpass shift.
  • Guaranteed 90% transmission with a typical transmission rate of 96%, these quality filters are parfocal and built to last without a tendency to scratch, be affected by moisture, or fade from age.


Astronomik 6 nm S-II MFR Narrowband Emissionline Filter
50 mm Round Unmounted

Astronomik SII Narrowband Filters are suitable for false color imaging of emission nebulae emanating singly ionized sulfur. The contrast between an object glowing at 672nm and the background is increased significantly due to the high transmission and effective out-of-band blocking!

The SII line (672 nm) is in the deep red portion of the spectrum, beyond H-alpha.

This Astronomik SII MFR Narrowband filter has a 6 nm FWHM. The extra narrow bandpass of 6 nm filters are most appreciated with cameras that offer extremely low dark current and good cooling, or when imaging in areas with severe light pollution. The higher level of out-of-band blocking allows you to take longer exposures and choose objects imbedded in normally over-bright, crowded areas of the Milky Way. Extra blocking causes faint stars to disappear from the background, and brighter stars will be pin-pricks of light.

Astronomik MFR Narrowband Emission Line Filter Highlights

    • Special Coatings Allow Filter Use Across Most Focal Ratios: Astronomik Narrowband Emissionline filters have been designed to be used with a wide range of focal ratios. The special MFR (multi-focal ratio) coatings applied to the 12 nm FWHM filters make them compatible with optics as fast as f/3, and the 6 nm models perform well with focal ratios as fast as f/4. This means you won’t need to buy different filters for your fast refractor and your SCT, and you won’t have to pay premium prices for “high speed” filters.


  • Amazingly High Out of Band Blocking: Astronomik Narrowband Emission-line Filters offer superb blocking of unwanted wavelengths, from UV up to IR. Transmission of 90% is guaranteed by Astronomik, but the typical transmission can be as high as 96% on both 6 nm and 12 nm Narrowband filters. This feature translates to extremely high contrast and pleasingly dark background skies, even under heavily light-polluted conditions, allowing you to take longer exposures if you so desire without creating an overly bright (or saturated) background. Another benefit of good out-of-band blocking is the reduction of stray light and haloes. Stars display as sharp points of light on a velvety black background, providing the perfect backdrop for the deep-sky object you are imaging.


    • Image During Full Moon or Under Light Polluted Skies: Because Astronomik Narrowband Emission Line Filters have a high transmission rate for the chosen wavelength but blocks pretty much everything else, you can image from your own backyard, even if your neighborhood suffers from light-pollution (which is pretty much everybody). If it’s a beautiful night with great seeing but the Moon phase doesn’t support visual deep-sky astronomy, you can pull out your telescope, camera, and Astronomik filters and still get great results.

Ten Year Warranty! Astronomik filters will last for many years without degradation of the coatings, due to the quality of the substrate and coatings used. The high-quality glass is optically polished and is free of stress and striae. The coatings used on Astronomik filters are applied in multiple layers, making the resulting filter scratch resistant and unaffected by moisture or aging that some filters of less quality may be prone to. Astronomik filters are also parfocal due to the small thickness tolerance allowed. Astronomik backs up this quality with a ten-year warranty.

Additional Information

Additional Information

Manufacturer Astronomik
Type of Filter Sulfur II
Filter Usage Imaging
Single or Set? Single Filter
Filter Size 50mm
Filter Shape Round
Filter Mounted? Unmounted
Warranty 10 Year Warranty
FWHM Bandwidth 6nm
Included Items

Included Items

  • Astronomik 6 nm SII CCD Filter with MFR Coatings - 50 mm Round Unmounted
  • Storage Box
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