This 52mm SLR Magic Self-Locking Variable ND Filter is a solid variable neutral density filter that is designed to mount onto lenses with 52mm front filter threads and provides an exposure reduction of 1.3 to 6 stops. The 0.4 to 1.8 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, helping you to predetermine 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 visually demarcated with numbers representing different density values and includes a rotation lever to further enable fast and precise positioning of the front ring. Once the front ring is rotated into a position that corresponds to the desired amount of density, the filter's rear ring can then be turned to lock the front ring into place, helping to ensure consistent exposures.