Orion 5579 1.25-Inch Sulfur-II Extra-Narrowband Filter Sulfur-II astrophotography filter allows high-contrast imaging even in light polluted skies Filter passes light at 672.4nm wavelength (S-II line) with a narrow bandpass of 7nm Very high 90&#37; transmission of S-II light allows stunning astrophotos to be captured in city skies 1.25" astrophotography filter made from high-grade glass with dichroic interference and antireflection coatings. Metal filter cell construction. Use with Orion O-III and H-alpha extra-narrowband imaging filters for tricolor CCD astrophotography