Optolong L-Pro (L-Professional) is a multi-bandpass filter which selectively suppresses the transmission of light pollution lines. For example, mercury vapor lamps, high and low pressure sodium vapor lights and skyglow caused by emission from neutral oxygen in our atmosphere. L-Pro enhances the transmission of major emissions from nebula while offering great color balance with its wide yet effective light pollution cutting transmission band. The balanced transmission allows objects with wide emission spectrum such as galaxies to be imaged with minimal color cast (easier to correct in post-processing). Among the emission lines enhanced are OIII (496, 500nm), H-beta (486nm), NII (654, 658nm), H-alpha (656nm) and SII (672nm). Available in 2", 1.25" and selected DSLR camera sizes. Features 90% transmission at major nebula emission lines Multi-layers anti-reflection coating Precise and sharp roll-off at light pollutant lines 2 mm filter thickness (1.25", 2" and 77mm) | 1mm (clip series) Made on Schott substrate Finely polished to 1/4 wave accuracy Surface quality: 60/40 (MIL-O-13830 standard) Best Uses Monochrome & one-shot-color CCD/CMOS camera Deep sky color imaging, particularly reflective nebula and galaxies