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 optical ...

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

Royal Photographic Society The Royal Photographic Society of Great Britain, commonly known as the Royal Photographic Society (RPS), is one of the world's oldest photographic societies. It was founded in London, England, in 1853 as the Photographic Society of London with ...

in 1910, some "debatants" held the use of such "graduated color screens" to be quite limited. In more modern times, the use of graduated ND filters was popularized by

Galen Rowell Galen Avery Rowell (August 23, 1940 – August 11, 2002) was a wilderness photographer, adventure photojournalist and mountaineer. Born in Oakland, California, he became a full-time photographer in 1972. Early life and education Rowell was in ...

. Singh-Ray sold them as "The Singh-Ray set of 4 Galen Rowell Graduated Neutral-Density Filters." Although its importance may have lessened with the advent of the modern

digital darkroom {{More citations needed, date=May 2008 Digital "darkroom" is the hardware, software and techniques used in digital photography that replace the darkroom equivalents, such as enlarging, cropping, dodging and burning, as well as processes that don't ...

, graduated ND filters are still an important tool for professionals because a digital sensor that is clipping ("blown out" or "washed out") captures no usable data in the clipped area, an effect which cannot be corrected with later processing because data has been lost.

Types

The filter comes in many types but can be separated into two basic categories: *Hard edge *Soft edge A hard edge is used when there is an abrupt change in brightness, such as a field with a horizon to a bright sky. A soft edge is a wider, smoother change from light to dark. This is used when the light and dark portions are not distinctly separated, such as a mountain and sky. A soft edge filter is less noticeable than a hard edge. It also has the benefit of making the sky more intense, darkening the sky the closer on the top. Below is a picture of what a hard edge and soft edge filter would look like.

Image:Grad-nd-soft-edge.svg, Soft-edge GND filter Image:Grad-nd-hard-edge.svg, Hard-edge GND filter

Multi-shoots high dynamic range

As an alternative to split graduated neutral density filters, some digital cameras offer built-in

high-dynamic-range imaging In photography and videography, multi-exposure HDR capture is a technique that creates extended or high dynamic range (HDR) images by taking and combining multiple exposures of the same subject matter at different exposure levels. Combining m ...

(HDR) which allow the camera to capture and then combine different exposures of the same subject matter when shooting in RAW image format. However, as long as a sufficiently short exposure time is available, it is possible to exactly mimic the effect of a graduated neutral density filter by using two exposures of the same scene one or several stops apart and blending them with a graduated mask in an image editor. This method has the advantage that the shape of the mask can be freely defined in editing. The disadvantage is that it only works with static subjects using a tripod.

References

External links

An effective demonstration picture
{{Commons category, Gradual ND filter, Graduated neutral density filter Optical filters