Optolong L-Ultimate dual-3nm filter
It's about a 3nm dual band designed to drastically reduce the effect of light pollution, the 3nm isolates the nebulae's emissions into H-Alpha (red) and OIII (green-blue). It blocks light pollution, maximizes the signal from nebulae, and darkens the sky background. It also blocks artificial light from mercury vapor lamps, high and low pressure sodium vapor lights, and unwanted natural light caused by the emission of neutral oxygen in our atmosphere. ...
