The Nano-X ND8 HD Green Multi-Coated Waterproof German Optics Schott B270 CPL Filter is a 72mm filter that adds a solid neutral density to the effect of a circular polarizer. When in use, this filter's 8x filter factor provides a 3-stop exposure reduction, darkening the entire image, allowing photographs to be made with a wider aperture or slower shutter speed than normally required. By slowing your exposure time or increasing the aperture, depth of field may be more finely controlled and movement more easily conveyed. Simultaneously, this filter can help reduce reflections and glare by filtering out light that has become polarized due to reflection from a nonmetallic surface. The light from the sun becomes partially polarized by reflecting off electrons in the air, causing light to scatter into what appears as haze. A polarizing filter arranges and filters this directionally polarized light perpendicularly to the reflected light, allowing for the absorption of much of this light. This results in a noticeable reduction in glare and reflections from nonmetallic surfaces and an increase in the saturation of skies and foliage. The combination of these two functions makes this an essential filter for landscape photography.