Hoya Variable ND filters provide a convenient way to adjust exposure control by varying the amount of light entering the camera by 1.5 to 9-stops (equivalent to NDx3-400 or 0.45-2.7 density). The precision double-ring design allows the outer ring to rotate, controlling the amount of neutral density anywhere within the 1.5 to 9-stop range. The thin double-ring design also reduces the likelihood of vignetting with wide-angle lenses. This versatile filter allows for many special effects such as being able to control depth of field by using a wider aperture or create or control motion blur by being able to choose slow shutter speeds for perfect blurring.