Optolong L-Ultimate filter 1.25" The L-Ultimate is a dual 3 nm narrowband filter passing only OIII (500.7 nm) and H-alpha (656.3 nm), for the darkest backgrounds and highest contrast in heavy light pollution. It is optimised to reduce halos around bright stars. Optolong notes it is not suited to fast focal-ratio systems.
Manufacturer model: Optolong L-Ultimate 1.25" · Specifications checked against manufacturer data on 2026-11-03
The L-Ultimate is a dual 3 nm narrowband filter passing only OIII (500.7 nm) and H-alpha (656.3 nm), for the darkest backgrounds and highest contrast in heavy light pollution. It is optimised to reduce halos around bright stars. Optolong notes it is not suited to fast focal-ratio systems.
| Format | 1.25" mounted |
|---|---|
| FWHM | OIII 3 nm; H-alpha 3 nm |
| Centre wavelengths | 500.7 nm; 656.3 nm |
| Substrate | Optical glass |
| Blocking range | 300–1000 nm |
| Blocking depth | >OD4 |
| Surface quality | 60/40 |
| Transmitted wavefront | λ/4 RMS |
| Parallelism | 30" |
| Optics | Not for fast focal-ratio systems |
Multi-layer anti-reflection coating on a non-cemented substrate, applied by ion-assisted deposition for durability and a stable centre wavelength with temperature.
Optolong L-Ultimate 1.25" mounted.
| Centre wavelengths | 500.7 nm; 656.3 nm |
|---|---|
| Blocking depth | >OD4 |
Data sheet
Optolong L-Ultimate filter 1.25" The L-Ultimate is a dual 3 nm narrowband filter passing only OIII (500.7 nm) and H-alpha (656.3 nm), for the darkest backgrounds and highest contrast in heavy light pollution. It is optimised to reduce halos around bright stars. Optolong notes it is not suited to fast focal-ratio systems.
Manufacturer model: Optolong L-Ultimate 1.25" · Specifications checked against manufacturer data on 2026-11-03
