All about S-II 4.5nm EDGE Antlia filters

The Antlia 4.5mm S-II filter is suitable for imaging diffuse nebulae, planetary nebulae and sulphide-2 rich supernovae remnants. The 4.5nm wide passband is centered on the SII line at 672nm. The thinness of the bandwidth allows deep sky imaging even in very difficult light pollution conditions and greatly increases the contrast of objects under very dark skies. All the parasitic lines of light pollution are eliminated, in particular those of mercury vapor and sodium lamps.

Antlia EDGE narrowband filters are designed to bring out the faintest details of nebulae by removing unwanted wavelengths from the sky background. The narrower the bandwidth, the more effective the filter. The transmission of the filters reaches 92% at 672nm. The optical density outside the transmission zone is OD5 (0.001%), which offers an excellent signal-to-noise ratio and a clean cut of the other lines. The clear cut of the signal outside the transmission zone is an important parameter since it conditions the quality of the filtration. The greater the cut-off slope, the greater the contrast between the S-II signal and the background of the sky which has become perfectly black. Additionally, a sharp cutoff minimizes halos around bright stars.

During manufacturing, Antlia carries out extremely strict quality control. Each filter is tested and measured to verify that it meets the high performance requirements of the specification. The low tolerances require the use of perfectly homogeneous substrates and a uniform thickness; deviation from specification shall not exceed 0.05mm.

The wavelength in nanometers is on the abscissa. The percentage of transmission is on the ordinate. The half-height transmission width is 4.5nm and the filter is centered at 672nm

Applications and performances

• Ultra-narrow 4.5nm bandwidth, designed for astronomical imaging of diffuse nebulae, planetary nebulae, and supernova remnants, regardless of sky quality
• Possibility of association with H-Alpha and O-III Antlia 4.5nm filters to obtain SHO images in Hubble palette
• Clean cut of unwanted lines around the S-II line. Transmission is 92% at 672nm and increases the contrast of SII emitting objects
• Antlia EDGE narrowband filters are compatible with instruments at F/d > 3 with slight signal loss
• All Antlia filters have blackened edges to suppress stray reflections
• Glass Type: Schott Optical Glass
• Surface quality: 60/40 (according to MIL-O-13830 standard)
• Substrate thickness 2mm
• Transmission 88% transmission on the S-II line (672nm)
• Treatments Polished filter on both sides with a precision of λ/4
• Multi-layer and anti-reflection treatments on both sides