Wratten numbers are a labeling system for

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 p ...

s, usually for photographic use comprising a number sometimes followed by a letter. The number denotes the color of the filter, but is arbitrary and does not encode any information (the 80A–80D are blue, the next filters in numerical order, 81A–81EF, are orange); letters almost always increase with increasing strength (the exception being 2B, 2A, 2C, 2E). They are named for the founder of the first photography company, British inventor Frederick Wratten. Wratten and partner C.E.K. Mees sold their company to

Eastman Kodak The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York, and is incorpor ...

in 1912, and Kodak started manufacturing Wratten filters. They remain in production, and are sold under license through the Tiffen corporation. Wratten filters are much used in

observational astronomy Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical m ...

by amateur astronomers. Color filters for visual observing made by GSO, Baader, Lumicon, or other companies are actually Wratten filters mounted in standard or 2 in (nominal, 48 mm actual) filter threads. For imaging

interference filter An interference filter or dichroic filter is an optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest. An interference filte ...

s are used. Wratten filters are also used in

photomicrography A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a mi ...

. Filters made by various manufacturers may be identified by Wratten numbers but not precisely match the spectral definition for that number. This is especially true for filters used for aesthetic (as opposed to technical) reasons. For example, an 81B warming filter is a filter used to slightly "

warm Warm, WARM, or Warmth may refer to: * A somewhat high temperature * Kindness Music * ''Warm'' (The Lettermen album), 1967, and the title song * ''Warm'' (Johnny Mathis album), 1958, and the title song * ''Warm'' (Herb Alpert album), 1969 * '' ...

" the colors in a color photo, making the scene a bit less blue and more red. Many manufacturers make filters labeled as 81B with

transmission curve The transmission curve or transmission characteristic is the mathematical function or graph that describes the transmission fraction of an optical or electronic filter as a function of frequency or wavelength. It is an instance of a transfer funct ...

s which are similar, but not identical, to the

Kodak The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York, and is incorpor ...

Wratten 81B. This is according to that manufacturer's idea of how best to warm a scene, and depending on the dyes and layering techniques used in manufacturing. Some manufacturers use their own designations to avoid this confusion, for example Singh-Ray has a warming filter which they designate A‑13, which is not a Wratten number. Filters used where precisely specified and repeatable characteristics are required, e.g. for printing press

color separation Color printing or colour printing is the reproduction of an image or text in color (as opposed to simpler black and white or monochrome printing). Any natural scene or color photograph can be optically and physiologically dissected into three ...

and scientific work, use more standardized and rigorous coding systems. Some filters are listed in tables of Wratten filters with codes which do not follow the original number-letter scheme, e.g. K2, G, X0, FL‑W; CC‑50Y. In digital photography, where the color temperature can be adjusted and color corrections can be easily accomplished in the camera (by firmware) or in software, the need for color filters has all but disappeared. Thus, it has become difficult to find Wratten filters in photography stores.

Reference table

The commonly available numbers and some of their uses include:

References

External links

* – Gives graphical spectral transmission curves for all Wratten filters available as of the publication date. * – Detailed compilation of numerical information on spectral transmission of Wratten filters, reproduced in the 90th CRC Handbook. * * * {{cite web , title=Color correction filters table , series=

Cokin Cokin is a French manufacturer of optical filters for photography. The system allows filters such as rectangular graduated neutral density filters which are versatile in use. History Cokin are particularly noted for their "Creative Filter Syst ...

Filter System , website=GeoCities , url=http://www.geocities.com/cokinfiltersystem/color_corection.htm , url-status=dead , archive-url=https://web.archive.org/web/20091028192325/http://www.geocities.com/cokinfiltersystem/color_corection.htm , archive-date=2009-10-28 Photography equipment Optical filters Encodings

Reference table

See also

References

External links