This filter is a 3nm dual band designed to drastically reduce the effect of light pollution and the 3nm isolate the nebulae's emissions into H-Alpha 656.3nm (red) and OIII 500.7 (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.