The Moon can be quite bright especially when gibbous or close to full, producing a lot of glare. This can dazzle the observer making it difficult to see fine detail. This filter reduces the brightness by 18% for more comfortable viewing. It also improves contrast so enhances surface features.
Due to the wavelengths of light passed this filter imparts a slight green tint.
Results depend on seeing conditions, the telescope and the target being observed or photographed but the right filter can make a significant difference when, for example, viewing the lunar surface or teasing detail from Jupiter’s weather bands or Saturn’s rings.