The Vivitar 40.5mm Variable NDX Filter is a solid variable neutral density filter providing a reduction in light by about 1 to 10 stops. The 0.3 to 3.0 (ND2-ND1000) density creates a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than normally required. The degree of density is easily controlled by rotating the front filter ring, allowing you to previsualize the additional exposure length required. By slowing your exposure time or increasing your aperture, you are able to control depth of field and convey movement more easily. For easier, repeatable control over density settings, the front ring is also visually demarcated with dots that each represent one stop of neutral density.