A graduated neutral-density filter, also known as a graduated ND filter, split neutral-density filter, or just a graduated filter, is an

optical filter An optical filter is a device that selectively transmits light of different wavelengths, usually implemented as a glass plane or plastic device in the optical path, which are either dyed in the bulk or have interference coatings. The optic ...

that has a variable light transmission. Typically half of the filter is of neutral density which transitions, either abruptly or gradually, into the other half which is clear. It is used to bring an overly-bright part of a scene into the

dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base- ...

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. ND filters can come in a variety of shapes and sizes and densities and can be used in all types of photographic applications from still photography, motion photography and scientific applications. Center-spot filters are ND graduated filters that are slightly opaque in the center and are clear at edges. These are used for special effects or to compensate for light falloff that is natural with large optics.

History

Graduated filters were used in the early twentieth century, for example for darkening skies in landscape photos. One advertised brand was called the "Lifa graduated filters for sky, cloud, and

landscape photography Landscape photography shows the spaces within the world, sometimes vast and unending, but other times microscopic. Landscape photographs typically capture the presence of nature but can also focus on man-made features or disturbances of landscapes ...

. These "sky filters" were not necessarily neutral, since they were used for

black-and-white Black-and-white (B&W or B/W) images combine black and white in a continuous spectrum, producing a range of shades of grey. Media The history of various visual media began with black and white, and as technology improved, altered to color. ...

photography, and sometimes used a yellow top half to darken blue skies more. In a discussion at the