High quality SII filter

This SII-CCD filter is suitable for imaging SII regions from observation sites with light pollution and dark sites as well. The contrast between a bright 672nm object and the background is increased enormously!

Due to the combination of the narrow bandwidth of 6nm and the high transmission of typically 96%, the filter gives you a huge contrast boost, as any unwanted light from other wavelengths than 672nm is blocked from UV to IR. This results in an extremely dark background.
The 6nm FWHM is tuned to give you optimal performance with CCD and CMOS sensors with very low dark current! The 6nm filter is the best choice if you are observing from a heavily light-polluted site or imaging faint objects in star-crowded regions of the Milky Way.

Thanks to the new MFR coating technique, you can use a single filter on all instruments up to f/4 without a significant reduction in performance.

Filter technical data:

• Guaranteed transmission of more than 90% on both SII lines (671.7 nm and 673.0 nm)
• 94% typical transmission on both SII lines (671.7 nm and 673.0 nm)
• Full Width Half Maximum (FWHM): 6nm
• perfect blocking of unwanted light from UV to IR
• parfokal with all Astronomik filters
• MFR coating technique: usable with all optics up to f/4
• 1mm thickness
• Not sensitive to moisture, scratch resistant, does not age
• Optically polished substrate, without streaks and without residual stresses
• High quality storage box

Imaging with narrowband emission line filters

If you have to observe from light-polluted sites (like most of us...), imaging with narrowband filters is the best way to take great images, because any kind of light pollution can be blocked very effectively! Normally an H-alpha filter should be your first step into this amazing field of astrophotography! With a narrowband H-alpha filter, you'll be able to take deep, high-contrast images even with very strong light pollution or with the full moon high in the sky!
If you look at other astrophotographs, an H-alpha is the best choice for all glowing nebulae! An OIII filter expands your imaging possibilities, as you are able to image all greenish/bluish structures. Planetary nebulae and star forming regions are excellent targets! SII filters complete your HSO filter set. With these three filters, you can process your images like those from the Hubble Space Telescope!


The h-beta filter is not available in a 6nm version, as this filter has almost no significant application. To illustrate this, two images are shown below: Both were taken with an unmodified Canon 650D. Even though the camera has less than 10% sensitivity at H-alpha, there is some signal and structure in the h-alpha image, whereas you can't see anything in the image taken with an H- filter. beta!

Filter Operation:

The filter blocks out any unwanted light from artificial light pollution, natural air glow and moonlight. In particular, light from high and low pressure sodium and mercury lamps and all lines of natural light are 100% blocked. The filter increases the contrast between the sky background and the objects that shine on the line xx to xy nm.

Tips and tricks for more applications:

Using the xx filter with the OIII-CCD and SII-CCD filters produces false color emission line (HSO) images similar to the Hubble-Space Telescope. This is possible even from heavily polluted sites!