For CCD astrophotography applications, this 36 mm SII 6 nm CCD Filter from Astronomik is the optimal narrowband filter. Features a reduced 6 nm FWHM (full width at half maximum) combined with a typical 96% transmission for an exceptional boost in contrast due to all unwanted light in wavelengths aside from SII being completely blocked from UV up to the IR. This results in a background that is extremely dark. Transmission reductions and chromatic distortions, which occur more often with other filters, only arise with Astronomik filters when especially bright 1:2 or more aperture ratios come into play.
Astronomik SII CCD filters highlight the contrast between objects that emit in the ionized sulfur (SII) line and the background sky. In addition, this filter serves as an excellent light pollution adversary as it obstructs artificial light from sources such as mercury and sodium vapor street lamps, as well as skyglow. The Astronomik SII CCD Filter's high quality substrate enables you to see needle sharp stars identical to those you would see via your regular telescope.
Complete blockage of all unwanted wavelengths in the visible and IR bands of the spectrum is enabled by the Astronomik 36 mm SII 6 nm CCD Filter. As with all filters from Astronomik, this filter is parfocal with all other Astronomik filters. It is also diffraction limited so it won't compromise the optical performance of your telescope. Coatings keep this SII CCD filter from inducing scratches and other damaging effects from aging and high humidity. All Astronomik filters are delivered in a long-lasting plastic filter case of supreme quality.