Filter ANTLIA SII 7nm PRIME model 36mm circular filter without mount

All you need to know about SII 7nm PRIME Antlia filters

The Antlia 7 mm SII Antlia filter is suitable for imaging diffuse nebulae, planetary nebulae and Sulfur-2-rich supernovae afterglows. The 7 nm bandwidth (centered on the SII line at 671.6 nm) gives PRIME filters a wider bandwidth than the EDGE range. Therefore, PRIME filters let a little more signal through... but a little more light pollution. The narrow bandwidth allows deep sky imaging even under very difficult light pollution conditions, and greatly increases the contrast of objects under very dark skies. A large proportion of stray light pollution lines, especially from mercury vapor and sodium lamps, are eliminated.

Antlia PRIME narrow band filters are designed to bring out the faintest details of nebulae by suppressing unwanted wavelengths from the sky background. The narrower the bandwidth, the more effective the filter. The transmission of the filter reaches 91% around 672 nm. The optical density outside the transmission area is OD4 (0.01%), 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 cutoff slope, the greater the contrast between the SII signal and the perfectly black background sky. In addition, a sharp cut-off minimizes halos around bright stars.

During the manufacturing process, Antlia performs extremely strict quality control. 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

• Narrow bandwidth of 7 nm, designed for astronomical imaging of planetary nebulae and supernova afterglow, whatever the sky quality.
• Can be combined with Antlia 7nm O-III and H-Alpha filters for SHO imaging in the Hubble palette
• Sharp cut-off of unwanted lines around SII. Transmission is 91% for lines at 671.6nm/672.4nm, increasing the contrast of objects with SII emission.
• Antlia EDGE narrowband filters are compatible with instruments at F/d >2 with slight signal loss.
• All Antlia filters have blackened edges to eliminate 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: 91% transmission on SII lines at 671.6nm and 672.4nm
• Treatments: 2-sided polished filter with λ/4 accuracy
• Coating: Multilayer and anti-reflective on 2 sides