Optolong L-eXtreme F2 2" dual-band narrowband filter for fast optical systems

Optolong L-eXtreme F2 2" filter is a dual-band filter for imaging emission nebulae with fast f/2–f/3.3 optical systems. It transmits selected H-alpha and OIII bands while reducing the contribution of sky background to the recorded image.

Key features

• two 7 nm bands for recording hydrogen and oxygen emission
• design intended for fast astrographs, including RASA and HyperStar systems
• multilayer coatings applied using the IAD process

Included items

• mounted Optolong L-eXtreme F2 2" filter

Technical specifications

• manufacturer: Optolong
• type: dual-band interference filter
• bands: H-alpha 656.28 nm and OIII 500.7 nm
• full width at half maximum, FWHM: 7 nm for each band
• optical system focal ratio range: f/2–f/3.3
• nominal size: 2"
• cell thread: M48 × 0.75
• glass thickness: 1.85 mm
• out-of-band blocking: OD > 4 over 300–1000 nm

In a fast nebula-imaging setup, the filter allows two emission lines to be recorded in a single exposure.