ALP-T Dual Band 3.5nm SII&H-beta Filter 2" Mounted

The Antlia ALP-T Dual Band 3.5nm SII & H‑beta is a 2" mounted narrowband filter engineered for colour (OSC) astrophotography. It transmits the Sulfur‑II line at 672.4 nm and the Hydrogen‑beta line at 486.1 nm while strongly suppressing out‑of‑band light to improve contrast and signal‑to‑noise on emission nebulae.

Key optical properties

With an ultra‑narrow full width at half maximum (FWHM) of 3.5 nm and high out‑of‑band optical density (reported OD ~4.5), the filter reduces light pollution, moonlight and airglow, isolating the SII and H‑beta emission lines for cleaner narrowband data on OSC cameras.

Imaging use and workflow

• Designed primarily for use with one‑shot colour cameras to capture SII and H‑beta simultaneously.
• When paired with a complementary Antlia ALP‑T Ha&OIII dual‑band filter, it enables capture of four narrowband channels (Ha, OIII, SII, H‑beta) for false‑colour or luminance‑enhanced composite images.
• Recommended for use with slower optics (f/4 or slower); Antlia notes a high‑speed pre‑shifted version is preferable for faster focal ratios.

Coatings and mechanical

• Double‑sided multi‑layer coatings applied by ion‑assisted deposition on a polished substrate to achieve stable bandpass and strong out‑of‑band suppression.
• Ultra‑thin 2" (M48×0.75) cell to minimise vignetting and a black anodised finish with laser engraving.

Safety and use notes: This filter is not for solar observation or visual use. Do not use for direct solar viewing.

Warning: Some manufacturer claims in the source mention specific performance details and recommended pairings. Where manufacturer data is not explicit in the supplied evidence, those points have been summarised from the source but any missing numeric specifications have been omitted below.