Wratten number
Encyclopedia
Wratten numbers are a labeling system for optical filters, 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 increase with increasing strength.
They are named for the man who founded the first company, Frederick Wratten
, a British inventor. Wratten and partner C. E. K. Mees sold their company to Eastman Kodak
in 1912, and Kodak started manufacturing Wratten filters, which remain in production, and are sold under license through the Tiffen
corporation.
Wratten filters are much used in observational astronomy
and photomicrography.
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" 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
s which are similar, bit not identical, to the Kodak Wratten 81B, according to that manufacturer's idea of how exactly it is best to warm a scene, and depending on their manufacturing techniques. 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 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 letter-number scheme, e.g. K2, G, X0, FL-W; CC-50Y.
They are named for the man who founded the first company, Frederick Wratten
Frederick Wratten
Frederick Charles Luther Wratten was an English inventor.Wratten started his career as a school teacher and organist, and moved to London in 1861 to become a clerk in the Photographic & Optical Warehouse owned by Joseph Solomon...
, a British inventor. Wratten and partner C. E. K. Mees sold their company to Eastman Kodak
Eastman Kodak
Eastman Kodak Company is a multinational imaging and photographic equipment, materials and services company headquarted in Rochester, New York, United States. It was founded by George Eastman in 1892....
in 1912, and Kodak started manufacturing Wratten filters, which remain in production, and are sold under license through the Tiffen
Tiffen
Tiffen Manufacturing Corporation is a company in Hauppauge, New York, U.S.A. which manufactures filters for photography, and other professional film and photography-related products. Founded in 1945, by Sol Tiffen, the company has won several Academy Awards for technical achievements infiltration...
corporation.
Wratten filters are much used in observational astronomy
Observational astronomy
Observational astronomy is a division of the astronomical science that is concerned with getting data, in contrast with theoretical astrophysics which is mainly concerned with finding out the measurable implications of physical models...
and photomicrography.
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" 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
Transmission curve
For an optical or electronic filter which is described by the fraction of its input that it transmits as a function of frequency or wavelength, the transmission curve or transmission characteristic is the mathematical function or graph that defines the transmission fraction as a function of...
s which are similar, bit not identical, to the Kodak Wratten 81B, according to that manufacturer's idea of how exactly it is best to warm a scene, and depending on their manufacturing techniques. Some manufacturers use their own designations to avoid this confusion, for example Singh-Ray
Singh-Ray
Singh-Ray Corporation, known as Singh-Ray Filters is an American maker of photographic filters based in Arcadia, Florida, and established in 1962.They are among the more expensive brands and have a reputation for high quality and personalized service...
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 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 letter-number scheme, e.g. K2, G, X0, FL-W; CC-50Y.
Reference table
The commonly available numbers and some of their uses include:| Wratten number | Visible color | Filter factor Filter factor In photography, filter factor refers to the multiplicative amount of light a filter blocks.-Converting between filter factors and stops:The table below illustrates the relationship between filter factor, the amount of light that is allowed through the filter, and the number of stops this... | F-Stops correction | Uses and characteristics |
|---|---|---|---|---|
| 1A | Called a skylight filter, this absorbs ultraviolet radiation, which reduces haze in outdoor landscape photography Landscape photography Landscape photography is a genre intended to show different spaces within the world, sometimes vast and unending, but other times microscopic. This popular style of photography is practiced by professionals and amateurs alike. Photographs typically capture the presence of nature and are often free... . |
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| 2A | pale yellow | Absorbs ultraviolet radiation. | ||
| 2B | pale yellow | Absorbs ultraviolet radiation, slightly less than #2A. | ||
| 2C | Absorbs ultraviolet radiation. | |||
| 2E | pale yellow | Absorbs ultraviolet radiation, slightly more than #2A. | ||
| 3 | light yellow | Absorbs excessive sky blue, making sky look slightly darker in black and white images. blocks visible wavelengths below 440nm | ||
| 4 | yellow | |||
| 6 | light yellow | |||
| 8 | yellow | K2 | Absorbs more blue than #3. | |
| 9 | deep yellow | Absorbs more blue than #8. blocks visible wavelengths below 465nm | ||
| 11 | yellowish-green | Color Correction. | ||
| 12 | deep yellow | Minus blue filter; complements #32 minus-green and #44A minus-red. Used with Ektachrome or Aerochrome Infrared films to obtain false-color results. Used in ophthalmology Ophthalmology Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems... and optometry Optometry Optometry is a health care profession concerned with eyes and related structures, as well as vision, visual systems, and vision information processing in humans. Optometrists, or Doctors of Optometry, are state licensed medical professionals trained to prescribe and fit lenses to improve vision,... in conjunction with a slit-lamp and a cobalt blue light to improve contrast when assessing the health of the cornea Cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is... and the fit of contact lenses. blocks visible wavelengths below 495nm |
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| 15 | deep yellow | Darkens the sky in black and white outdoor photography. blocks visible wavelengths below 505nm | ||
| 16 | yellow-orange | Like #15, but more so. blocks visible wavelengths below 520nm | ||
| 18A | visually opaque | Based on Wood's glass Wood's glass Wood's glass is an optical filter glass invented by American physicist Robert Williams Wood which allows ultraviolet and infrared light to pass through while blocking most visible light. It was developed as a light filter used in communications during World War I... , transmits small bands of ultraviolet Ultraviolet Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV... radiation and infrared Infrared Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm... radiation. |
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| 18B | very deep violet | Similar to 18A but with wider bands of transmittance in both the ultraviolet Ultraviolet Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV... and infrared Infrared Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm... , a less 'pure' filter. |
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| 21 | orange | G | Contrast filter for blue and blue-green absorption. blocks visible wavelengths below 530nm | |
| 22 | deep orange | Contrast filter, greater effect than #21. blocks visible wavelengths below 550nm | ||
| 23A | light red | blocks below 560nm | ||
| 24 | red | Used for color separation of Kodachrome tranparency film, complements #47B and #61. | ||
| 25 | red tricolor | Used for color separation and infrared photography Infrared photography In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about... blocks below 580nm. |
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| 25A | red | 8 | 3 | Strong contrast red filter used for color separation and infrared photography Infrared photography In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about... in black and white film and blocks below 580nm. |
| 26 | red | |||
| 29 | deep red | Used for color separation, complements #47 and #61. In black and white outdoor photography makes blue skies look very dark, almost black. In infrared photography, blocks much visible light, increasing the effect of the infrared frequencies on the picture. blocks below 600nm. | ||
| 32 | magenta | Minus-green. Complements #12 minus-blue and #44A minus-red. | ||
| 34A | violet | Used for minus-green and plus-blue separation. | ||
| 38A | blue | Absorbs red, some UV and some green light. | ||
| 44 | light blue-green | minus-red filter with much UV absorption. | ||
| 44A | light blue-green | minus-red, complements #12 is minus-blue and #32 minus-green. | ||
| 47 | blue tricolor | Used for color separation. Complements #29 and #61. | ||
| 47A | light blue | By removing lots of light that is not blue, blue and purple objects show a broader range of colors. Used for medical applications that involve making dyes fluoresce. | ||
| 47B | deep blue tricolor | Used for color separation. It is also commonly used to calibrate video monitors while using SMPTE color bars. | ||
| 50 | deep blue | |||
| 56 | light green | |||
| 58 | green tricolor | Color separation. | ||
| 61 | deep green tricolor | Color separation, complements #29 and #47. | ||
| 70 | red | Used for color separation and infrared photography Infrared photography In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about... blocks below 645nm. |
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| 80A | blue | 4 | 2 | Color Conversion. Raises the color temperature Color temperature Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, and other fields. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of... , causing a 3200 K tungsten-lit scene to appear to be daylight lit, approximately 5500 K. This allows use of a daylight balanced film with tungsten lighting. |
| 80B | blue | 3 | 1+2/3 | Similar to 80A; 3400 K to 5500 K. |
| 80C | blue | 2 | 1 | Similar to 80A; 3800 K to 5500 K. Typically used so that old-style flashbulb Flashbulb Flashbulb may refer to:*Flash photography*The Flashbulb, one of the pseudonyms of electronica musician Benn Jordan*"Flashbulb", a bonus track by Nirvana... s can be used on a daylight film. |
| 80D | blue | 1.5 | 1/3 | Similar to 80A; 4200 K to 5500 K. |
| 81A | pale orange | 1.4 | 1/3 | Warming filter to decrease the color temperature slightly; this can also be used when shooting tungsten type B film (3200 K) with 3400 K photoflood lights. The opposite of 82A. |
| 81B | pale orange | 1.4 | 1/3 | Warming filter, slightly stronger than 81A. The opposite of 82B. |
| 81C | pale orange | 1.5 | 1/3 | Warming filter, slightly stronger than 81B, opposite of 82C. |
| 81D | pale orange | Warming filter, slightly stronger than 81C. | ||
| 81EF | pale orange | 1/3 | Warming filter, stronger than 81D. | |
| 82A | pale blue | 1.3 | 1/3 | Cooling filter to increase the color temperature slightly. The opposite of 81A. |
| 82B | pale blue | 1.4 | 2/3 | Cooling filter, slightly stronger than 82A and opposite of 81B. Can also be used when shooting tungsten type B film (3200 K) with household 100 W electric bulbs (2900 K). |
| 82C | pale blue | 1.5 | 2/3 | Cooling filter, slightly stronger than 82B and opposite of 81C. |
| 85 | amber | 1.5 | 2/3 | Color conversion, the opposite of the 80A; this is a warming filter that takes an outdoor scene lit by sunlight (which has a color temperature around 5500 kelvin Kelvin The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all... s) and makes it appear to be lit by tungsten incandescent bulbs around 3400 K. This allows an indoor balanced film to be used to photograph outdoors. These filters were used in Super 8 movie cameras that were designed to use Tungsten film. |
| 85B | amber | 1.5 | 2/3 | Similar to 85; converts 5500 K to 3200 K. |
| 85C | amber | 1.5 | Similar to 85; converts 5500 K to 3800 K. | |
| 85N3 | amber | Neutral density of 1 stop + color conversion, the opposite of the 80A; this is a warming filter that takes an outdoor scene lit by sunlight (which has a color temperature around 5500 kelvin Kelvin The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all... s) and makes it appear to be lit by tungsten incandescent bulbs around 3400 K. This allows an indoor balanced film to be used to photograph outdoors. |
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| 85N6 | amber | Neutral density of 2 stops + color conversion, the opposite of the 80A; this is a warming filter that takes an outdoor scene lit by sunlight (which has a color temperature around 5500 kelvins) and makes it appear to be lit by tungsten incandescent bulbs around 3400 K. This allows an indoor balanced film to be used to photograph outdoors. | ||
| 85N9 | amber | Neutral density of 3 stops + color conversion, the opposite of the 80A; this is a warming filter that takes an outdoor scene lit by sunlight (which has a color temperature around 5500 kelvins) and makes it appear to be lit by tungsten incandescent bulbs around 3400 K. This allows an indoor balanced film to be used to photograph outdoors. | ||
| 87 | opaque | Passes infrared but not visible frequencies. blocks wavelengths below 740nm | ||
| 87A | opaque | Passes infrared but not visible frequencies. blocks wavelengths below 880nm | ||
| 87B | opaque | Passes infrared, blocks visible frequencies. blocks wavelengths below 820nm | ||
| 87C | opaque | Passes infrared, blocks visible frequencies. blocks wavelengths below 790nm | ||
| 88 | opaque | Passes infrared, blocks visible wavelengths below 700nm. | ||
| 88A | opaque | Passes infrared, blocks visible frequencies. below 720nm. | ||
| 89B | near-opaque red | R72 | Passes infrared, blocks visible wavelengths below 680nm (very dark red). Aerial photography Aerial photography Aerial photography is the taking of photographs of the ground from an elevated position. The term usually refers to images in which the camera is not supported by a ground-based structure. Cameras may be hand held or mounted, and photographs may be taken by a photographer, triggered remotely or... is one use. |
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| 90 | dark grayish amber | Used for viewing scenes without color before photographing them, in order to assess the brightness values. Not used for actual photography. | ||
| 92 | red | color densitometry. | ||
| 93 | green | color densitometry. | ||
| 94 | blue | color densitometry. | ||
| 96 | grayish | varies | neutral density filter Neutral density filter In photography and optics, a neutral density filter or ND filter can be a colorless or grey filter. An ideal neutral density filter reduces and/or modifies intensity of all wavelengths or colors of light equally, giving no changes in hue of color rendition.The purpose of standard photographic... . Blocks all frequencies of light evenly, making scene darker overall. Available in many different values, distinguished by optical density or by filter factor Filter factor In photography, filter factor refers to the multiplicative amount of light a filter blocks.-Converting between filter factors and stops:The table below illustrates the relationship between filter factor, the amount of light that is allowed through the filter, and the number of stops this... . |
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| 98 | blue | Like a #47B plus a #2B filter. | ||
| 99 | green | Like a #61 plus a #16 filter. | ||
| 102 | yellow-green | Color conversion; makes a barrier-level type photocell respond as a human eye would. | ||
| 106 | amber | Color conversions; makes an S-4 type photocell respond as a human eye would. |