Filter ANTLIA SII 4.5nm EDGE model 36mm circular unmounted filter

All you need to know about Antlia S-II 4.5nm EDGE filters

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

Antlia EDGE narrow band 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. Filter transmission reaches 92% at 672 nm. The optical density outside the transmission zone is OD5 (0.001%), which provides an excellent signal-to-noise ratio and a clear cut-off of the other lines. The clear cut-off of the signal outside the transmission zone is an important parameter because it determines the quality of the filtration. The steeper the cut-off slope, the higher the contrast between the S-II signal and the perfectly black background sky. In addition, a sharp cut-off minimizes halos around bright stars.

Antlia conducts extremely strict quality control during the manufacturing process. Each filter is tested and measured to ensure that it meets the high performance requirements of the specifications. Tight tolerances require perfectly homogeneous substrates and uniform thicknesses; deviations from specifications should not exceed 0.05 mm.

Applications and performance

• Very narrow bandwidth of 4.5 nm, designed for astronomical imaging of diffuse nebulae, planetary nebulae and supernova afterglow, whatever the sky quality.
• Can be combined with the 4.5nm H-Alpha and O-III Antlia filters for SHO imaging in the Hubble palette
• Sharp cut-off of unwanted lines around the S-II line. Transmission is 92% at 672nm, which increases the contrast of objects with SII emission.
• 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.

Technical specifications:

• Glass type: Schott optical glass
• Surface quality: 60/40 (according to MIL-O-13830)
• Mounting diameter: 36mm circular without mount
• Substrate thickness: 2 mm
• Transmission: 88% on S-II line (672nm)
• Treatments: 2-sided polished filter with λ/4 accuracy
• Coating: multilayer and anti-reflective on 2 sides