Altair 3.5nm DualBand SII–OIII ULTRA Filter (with Individual Spectrographic Test Report)

• Push through city glow and bright Moon with ultra-narrow 3.5 nm FWHM passbands that isolate SII 671.6 nm and OIII 500.7 nm for striking bi-color images from OSC or mono rigs.

• Real, per-filter data: each unit ships with its own 0.1 nm-resolution spectrograph report (not a batch average) so you know the exact CWL, FWHM, and peak transmission.

• Jet-black backgrounds: average OD6 blocking (~0.0001%) across unwanted wavelengths suppresses airglow, LED spill, and gradients while preserving faint nebular structure.

• High transmission where it counts: ~90–95% peak T in both bands plus halo-suppression AR coatings and SiO₂ hard overcoat for tight stars and durable performance.

• Flexible capture workflows: run bi-color in one exposure on OSC for faster integrations, or pair with a Ha–OIII DualBand or single-line Ha to build full palettes with minimal filter swaps.

• DSLR and astro-CMOS friendly: integrated UV/IR block ensures clean stars on refractors; works with modified and unmodified DSLRs and high-QE OSC cameras.

• Drop-in compatibility: 2" mounted (M48×0.75) fits Altair magnetic holders, standard 2" wheels/drawers, and Altair Canon/Nikon lens-to-CMOS adapters; parfocal 1.85 mm glass eases swapping.

Specifications

• Type: Dual-band ultra-narrowband (SII + OIII)

• OIII Band: CWL 500.7 nm, FWHM ~3.5 nm (tolerance ~±0.2 nm), T ~90–95%

• SII Band: CWL 671.6 nm, FWHM ~3.5 nm (tolerance ~±0.2 nm), T ~90–95%

• Blocking: Average OD6 over the majority of out-of-band visual wavelengths

• Optics: 1.85 mm parfocal glass, ~30 arcsec parallelism

• Coatings: UV/IR block, anti-reflection halo-suppression, SiO₂ hard overcoat

• Cell/Thread: 2" mounted, M48×0.75

• Cameras: OSC CMOS, mono CMOS/CCD, modified & unmodified DSLRs

• Use Cases: Extreme light pollution, bright-Moon sessions, short summer twilights, fast bi-color mapping

What’s in the box?

• Altair 3.5nm DualBand SII–OIII ULTRA 2" filter (M48×0.75)

• Individual spectrographic test report for this exact filter