The Optolong L-Ultimate 1.25" (Optolong, SKU: L-ULTIMATE-125) is an advanced dual narrowband filter featuring an ultra-narrow 3 nm bandpass, designed to drastically reduce light pollution and significantly improve contrast in emission nebula astrophotography.

Key features

• ultra dual narrowband filter with 3 nm bandwidth
• isolates H-alpha (656.3 nm) and O-III (500.7 nm) emission lines
• effective suppression of light pollution and darker sky background
• improved contrast and signal-to-noise ratio
• minimized halos around bright stars

Main use and performance

• designed for narrowband imaging of emission nebulae
• suitable for DSLR cameras and dedicated mono or color CCD and CMOS cameras
• effectively blocks artificial light from mercury vapor and high- and low-pressure sodium lamps
• suppresses unwanted natural skyglow caused by atmospheric oxygen emission
• not recommended for use with fast optical systems

Technical specifications

• diameter: 1.25"
• filter type: dual narrowband
• FWHM: 3 nm (H-alpha and O-III)
• blocking range: 300–1000 nm
• blocking level: >OD4
• substrate material: B270 optical glass
• glass thickness: 1.85 mm
• surface quality: 60/40
• transmitted wavefront RMS: λ/4
• parallelism: 30 arcseconds
• more than 150 coating layers
• mounted filter
• supplied in a protective plastic case with EVA foam lining