Chroma H-alpha 3 nm 2" (27001) — ultra-narrowband, M48 threaded ring The Chroma 27001 H-alpha 3 nm bandpass filter isolates the 656.3 nm hydrogen-alpha line, essential for imaging nebulae rich in ionised hydrogen. Its ultra-narrow passband separates H-alpha from the nearby SII doublet and gives maximum contrast and background suppression, even under…
Manufacturer model: Chroma 27001 H-alpha 3nm, 2-inch M48 threaded ring · Specifications checked against manufacturer data on 2026-11-03
The Chroma 27001 H-alpha 3 nm bandpass filter isolates the 656.3 nm hydrogen-alpha line, essential for imaging nebulae rich in ionised hydrogen. Its ultra-narrow passband separates H-alpha from the nearby SII doublet and gives maximum contrast and background suppression, even under light pollution or bright moonlight.
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 to f/5. For systems around f/3, Chroma offers a separate f/2.8–f/3.6-optimised version (27065).
| Chroma part number | 27001 H-alpha 3nm Bandpass |
|---|---|
| Target line | H-alpha, 656.3 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 H-alpha filters · Chroma f/# performance data
Standard 27001, not the f/2.8–f/3.6 optimised 27065. Chroma catalogue CWL field reads 650 nm; filter targets 656.3 nm line.
| Target line (nm) | 656.3 |
|---|---|
| Published fnumber data | Collimated, f/2 to f/5 |
Data sheet
Chroma H-alpha 3 nm 2" (27001) — ultra-narrowband, M48 threaded ring The Chroma 27001 H-alpha 3 nm bandpass filter isolates the 656.3 nm hydrogen-alpha line, essential for imaging nebulae rich in ionised hydrogen. Its ultra-narrow passband separates H-alpha from the nearby SII doublet and gives maximum contrast and background suppression, even under…
Manufacturer model: Chroma 27001 H-alpha 3nm, 2-inch M48 threaded ring · Specifications checked against manufacturer data on 2026-11-03
