Optolong SII CCD 6.5nm Narrowband Filter 31mm Unmounted for Astrophotography - Perfect for Deep Sky Imaging and Nebula Photography

The top-performing Sulfur II is an Extra-Narrowband Filter designed by Optolong that transmits a 6.5nm bandwidth of light, centered at 672nm and measures 36mm in diameter. This filter also greatly lessens other wavelengths passing through, including wavelengths notorious for light pollution (both artificial and natural). Like all Optolong filters with the “CCD” designation, this SII filter also blocks infrared wavelengths from 700nm to 1100nm so you don't need a separate IR-Cut filter.

The Optolong 6.5nm SII filter can be used in conjunction with H-Alpha and OIII filters for false color emission line images like the Hubble Space Telescope.

Due to the narrow bandwidth and high transmission rate of this filter, you will experience a major boost to contrast. The sky will be black, and when compared to a 12nm SII, half as many stars will peep through. Extra Narrowband filters work best with cameras that have very low dark current but will allow you to image from sites with lots of light pollution.

The Optolong 31mm Unmounted SII 6.5nm Filter is made with Schott glass that has been multi-coated with an ion-assisted deposition technology to ensure scratch resistance and stability on the central wavelength or CWL. This 6.5nm SII filter is designed to be used in filter wheels that accept 31mm unmounted filters in a round format.

Quality Filter Materials:

• Schott B260 substrate material from Germany, 2.0mm thick

• Multiple layers of anti-reflection non-cementing coatings applied via electron-beam gun evaporation with Ion-assisted deposition

Optolong Filter Manufacturing Processes and Parameters

• Filter substrate is fine-optically polished to 1/4 wave and <30 parallelism over both surfaces

• Surface quality, according to MIL-O-13830, is 60/40

• 80% transmission at SII line 672nm

• Infrared wavelength 700-1100nm cut-off

• 0.1% transmission Hg at 435nm and 578nm

• 0.1% transmission Na at 589nm

• High-value transmission of pass-band and optical density of off-band is assured through Optolong’s planetary rotation system, a homogeneous and precise coating procedure

• Each filter comes with a plastic case with high-pressure EVA case lining

About Optolong

Optolong is the Astronomy Filters division of Yulong Optics, an optical filter design, and processing company out of Kunming, China that has provided filters for over 700 optical companies since 1999. All Optolong filters pass European Union RoHS requirements and have been certified by TUV Rheinland and Bureau Veritas.