A graduated neutral density filter, also known as a graduated ND filter, gradual grey filter, split neutral density filter, or just a graduated filter, GND, is an optical filter that has a variable light transmission. * Typically half of the filter is of neutral density which transits gradually into the other half which is clear. * . It is used to bring an overly bright part of a scene into the dynamic range of film or sensor. For example, it can be used to darken a bright sky so that both the sky and subject can be properly exposed. * The filter is similar to half-color, except that color density gradually decreases near the center of the filter allowing emphasis of foregrounds or backgrounds. * Mounted in a rotating frame allows you to get appropriate angle for photography and choose any part of the scene to be effected.