Chroma SII 3 nm 2" (27009) — ultra-narrowband, M48 threaded ring The Chroma 27009 SII 3 nm bandpass filter isolates the emission of singly ionised sulphur, a doublet at 671.6 nm and 673.1 nm common in nebulae. It also separates sulphur emission from the nearby H-alpha line at 656.3 nm, completing a sharp SHO narrowband palette.
Manufacturer model: Chroma 27009 SII 3nm, 2-inch M48 threaded ring · Specifications checked against manufacturer data on 2026-11-03
The Chroma 27009 SII 3 nm bandpass filter isolates the emission of singly ionised sulphur, a doublet at 671.6 nm and 673.1 nm common in nebulae. It also separates sulphur emission from the nearby H-alpha line at 656.3 nm, completing a sharp SHO narrowband palette.
Made on a single high-grade glass substrate with hard sputtered coatings and no lamination, the filter withstands humidity and temperature extremes. The primary coating is on the front and an AR coating on the back to prevent ghosts. Chroma publishes measured spectral data for this filter collimated and at f/2.5 to f/5.
| Chroma part number | 27009 SII 3nm Bandpass |
|---|---|
| Target lines | SII doublet, 671.6 nm and 673.1 nm |
| Bandwidth | 3 nm |
| Format | 2-inch M48 threaded ring |
| Coating | Hard sputtered; AR-coated back face |
| Substrate | Single glass substrate; 3 mm thick (Chroma astronomy brochure) |
| Recommended focal ratio | f/4 and slower for this standard version |
Chroma 27009 SII 3nm · Chroma f/# performance data
Standard 27009. Chroma catalogue CWL field reads 670 nm; filter targets the 671.6/673.1 nm doublet.
| Target lines (nm) | 671.6; 673.1 |
|---|---|
| Published fnumber data | Collimated, f/2.5 to f/5 |
Data sheet
Chroma SII 3 nm 2" (27009) — ultra-narrowband, M48 threaded ring The Chroma 27009 SII 3 nm bandpass filter isolates the emission of singly ionised sulphur, a doublet at 671.6 nm and 673.1 nm common in nebulae. It also separates sulphur emission from the nearby H-alpha line at 656.3 nm, completing a sharp SHO narrowband palette.
Manufacturer model: Chroma 27009 SII 3nm, 2-inch M48 threaded ring · Specifications checked against manufacturer data on 2026-11-03
