The Urth 77mm ND2-400 (1-8.6 Stop) Variable ND Lens Filter is a variable neutral density filter that reduces light by 1 to 8.6 f-stops, giving you more creative control under different lighting conditions. By blocking the light by 1 to 8.6 f-stops you can use a larger aperture or slower shutter speeds. This way you create a smaller depth of field or long exposure effects by using longer shutter speeds without overexposed images.