The Antlia SII 3nm Pro Highspeed 1.25" 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 ensures strong SII contrast and excellent signal-to-noise performance even under light-polluted skies.

Key features

• optimized for f/2.6–f/3.6 optical systems through a pre-shifted central wavelength
• 3 nm FWHM providing very high contrast in the SII emission line
• peak transmission of about 90%
• compensation of blue-shift effects characteristic of fast optical systems
• off-band blocking to at least OD5 (0.001%) from 300–1000 nm
• single-substrate construction minimizing internal reflections and halos
• ultra-thin 1.25" filter cell reducing vignetting
• black anodized cell with laser-engraved, non-fading markings
• suitable for imaging emission nebulae, planetary nebulae and supernova remnants
• suitable for both light-polluted and dark skies, including bright-Moon conditions
• not intended for visual observing or for solar observing
• manufacturer warranty: 3 years against coating delamination

Included items

• Antlia SII 3nm Pro Highspeed 1.25" filter in M28.5×0.6 threaded cell

Technical specifications

• filter type: narrowband, sulfur SII line
• diameter: 1.25"
• thread: M28.5×0.6
• full-width at half maximum (FWHM): 3 nm
• central wavelength (CWL): 673.6 nm (pre-shifted for fast optical systems)
• peak transmission: about 90%
• off-band blocking: at least OD5 between 300–1000 nm
• recommended focal ratio: f/2.6–f/3.6
• applications: imaging emission nebulae, planetary nebulae, supernova remnants
• substrate: single optical-grade, non-glued
• surface quality: scratch/dig 60/40 (MIL-O-13830)
• transmitted wavefront: λ/4 or better
• parallelism: <30″ (arcseconds)
• filter thickness (1.25" mounted): 2.0 mm ±0.05 mm
• not recommended uses: visual observing, solar observing

Warning: NEVER look at the Sun through the Antlia SII 3nm Pro Highspeed 1.25" filter. Ignoring this warning can cause permanent eye damage.