The Antlia SII 3nm Pro Highspeed 50 mm is a narrowband imaging filter designed for fast optical systems with focal ratios between f/2.6 and f/3.6. Its pre-shifted central wavelength provides excellent SII emission contrast and a high signal-to-noise ratio even under light-polluted skies.

Key features

• optimized for f/2.6–f/3.6 optical systems thanks to the pre-shifted central wavelength
• 3 nm FWHM delivering high contrast in the SII emission line
• peak transmission of about 90%
• compensation of blue-shift effects typical of fast optical systems
• off-band blocking to at least OD5 (0.001%) from 300–1000 nm
• single-substrate optical construction minimizing internal reflections and halos
• blackened edges reducing stray-light reflections (unmounted filter)
• high optical stability reducing the need for extensive post-processing
• suitable for imaging emission nebulae, planetary nebulae and supernova remnants
• effective under both light-polluted and dark skies, including bright Moon conditions
• not intended for visual observing or for solar observation
• manufacturer warranty: 3 years against coating delamination

Included items

• Antlia SII 3nm Pro Highspeed 50 mm unmounted filter with blackened edges

Technical specifications

• filter type: narrowband, sulfur SII
• diameter: 50 mm (unmounted)
• full-width at half maximum (FWHM): 3 nm
• central wavelength (CWL): 673.6 nm (pre-shifted for fast systems)
• peak transmission: about 90%
• off-band blocking: ≥ OD5 (300–1000 nm)
• recommended focal ratio: f/2.6–f/3.6
• applications: emission nebulae, planetary nebulae, supernova remnants
• substrate: single optical-grade, non-glued
• edge treatment: blackened edges
• surface quality: scratch/dig 60/40 (MIL-O-13830)
• transmitted wavefront: λ/4 or better
• parallelism: <30″ (arcseconds)
• thickness: 3.0 mm ±0.05 mm
• not recommended uses: visual observing, solar observing

Warning: NEVER look at the Sun through the Antlia SII 3nm Pro Highspeed 50 mm filter. Ignoring this warning can cause permanent eye damage.