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.
Specifications
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
Coating
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 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
