Antlia SII 2.5 nm Ultra Narrowband — 2" mounted Antlia's 2.5 nm Ultra series is its narrowest narrowband line. This SII filter isolates the 671.6 / 673.1 nm sulphur doublet, cleanly separated from H-alpha, to complete an SHO set with maximum contrast.
Manufacturer model: Antlia SII 2.5nm Ultra, 2-inch mounted · Specifications checked against manufacturer data on 2026-11-03
Antlia's 2.5 nm Ultra series is its narrowest narrowband line. This SII filter isolates the 671.6 / 673.1 nm sulphur doublet, cleanly separated from H-alpha, to complete an SHO set with maximum contrast.
The filter is made on 2 mm quartz-glass substrate, held to ±0.05 mm, and blocks out-of-band light to OD5. Antlia recommends it for optics at f/3.5 and slower.
| Lines | SII, 671.6 nm and 673.1 nm |
|---|---|
| Bandwidth (FWHM) | 2.5 nm (+0.3 / −0.1 nm) |
| Peak transmission | At least 95% |
| Blocking | OD5 minimum |
| Substrate | Quartz glass, 2 mm ±0.05 mm |
| Recommended focal ratio | f/3.5 and slower |
| Format | 2-inch mounted |
Antlia 2.5 nm Ultra narrowband filters
2.5 nm Ultra series. f/3.5 and slower.
| Peak transmission min (%) | 95 |
|---|
Data sheet
Antlia SII 2.5 nm Ultra Narrowband — 2" mounted Antlia's 2.5 nm Ultra series is its narrowest narrowband line. This SII filter isolates the 671.6 / 673.1 nm sulphur doublet, cleanly separated from H-alpha, to complete an SHO set with maximum contrast.
Manufacturer model: Antlia SII 2.5nm Ultra, 2-inch mounted · Specifications checked against manufacturer data on 2026-11-03
