Antlia OIII 2.5 nm Ultra Narrowband — 2" mounted Antlia's 2.5 nm Ultra series is its narrowest narrowband line. This OIII filter isolates the 500.7 nm doubly ionised oxygen line for maximum contrast and star-size control, even under heavy light pollution or a bright Moon.
Manufacturer model: Antlia OIII 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 OIII filter isolates the 500.7 nm doubly ionised oxygen line for maximum contrast and star-size control, even under heavy light pollution or a bright Moon.
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.
| Line | OIII, 500.7 nm |
|---|---|
| Bandwidth (FWHM) | 2.5 nm (+0.3 / −0.1 nm) |
| Peak transmission | At least 92% |
| 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, not 3 nm Pro or 4.5 nm Edge. f/3.5 and slower. Cell dimensions not published.
| Peak transmission min (%) | 92 |
|---|
Data sheet
Antlia OIII 2.5 nm Ultra Narrowband — 2" mounted Antlia's 2.5 nm Ultra series is its narrowest narrowband line. This OIII filter isolates the 500.7 nm doubly ionised oxygen line for maximum contrast and star-size control, even under heavy light pollution or a bright Moon.
Manufacturer model: Antlia OIII 2.5nm Ultra, 2-inch mounted · Specifications checked against manufacturer data on 2026-11-03
