Wratten number
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 almost always increase with increasing strength (the exception being 2A, 2B, 2C, 2E).
Kodak Wratten filter 80A in its original packaging
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 in 1912, and Kodak started manufacturing Wratten filters. They remain in production, and are sold under license through the Tiffen corporation.[1]
Wratten filters are much used in observational astronomy by amateur astronomers. Color filters for visual observing made by GSO, Baader, Lumicon, or other companies are actually Wratten filters mounted in standard 1 1⁄4 in (32 mm) or 2 in (nominal, 48 mm actual) filter threads. For imaging interference filters are used. Wratten filters are also used in photomicrography.[2]
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 curves which are similar, but not identical, to the Kodak Wratten 81B. This is according to that manufacturer's idea of how 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;[3] CC-50Y.[4]
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:
| Wratten number | Visible color | Filter factor or alternate designation | F-Stops correction | Uses and characteristics |
|---|---|---|---|---|
| 1A | Called a skylight filter, this absorbs ultraviolet radiation, which reduces haze in outdoor color landscape photography; darkens the blue sky and by contrast lightens clouds. | |||
| 2A | pale yellow | Absorbs ultraviolet radiation and heightens contrast of clouds against blue sky. Longpass filter blocking wavelengths below 405 nm. Used for high-altitude photography. | ||
| 2B | pale yellow | Absorbs ultraviolet radiation, slightly less than #2A. Longpass filter blocking wavelengths below 395 nm. Used for high-altitude photography. | ||
| 2C | Absorbs ultraviolet radiation. Longpass filter blocking wavelengths below 390 nm. Used for high-altitude photography. | |||
| 2E | pale yellow | Absorbs ultraviolet radiation, slightly more than #2A. Longpass filter blocking wavelengths below 415 nm. Used for high-altitude photography. | ||
| 3 | light yellow | Absorbs excessive sky blue, making sky look slightly darker in black & white images. Can be used with carefully chosen color film, or with color balancing during printing, to heighten contrast of clouds against blue sky. Longpass filter blocking wavelengths below 440 nm. Used for high-altitude photography. | ||
| 4 | yellow | Longpass filter blocking visible wavelengths below 455 nm. Used for high-altitude photography. | ||
| 6 | light yellow | K1 | Not a longpass filter | |
| 8 | yellow | K2 | 1 | Absorbs more blue than #3. Longpass filter blocking visible wavelengths below 465 nm |
| 9 | deep yellow | K3 | Absorbs more blue than #8. Longpass filter blocking visible wavelengths below 470 nm | |
| 11 | yellowish-green | X0 | 2 | Heightens contrast of skin tones in black & white photography. Not a longpass filter |
| 12 | deep yellow | Minus blue | 1+1/3 | 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 and optometry in conjunction with a slit-lamp and a cobalt blue light to improve contrast when assessing the health of the cornea and the fit of contact lenses. Longpass filter blocking visible wavelengths below 500 nm |
| 13 | Green | 2 | Color enhancement. Not a long-pass filter | |
| 15 | deep yellow | G | 1+2/3 | Profoundly darkens the sky in black & white outdoor photography. Longpass filter blocking visible wavelengths below 510 nm |
| 16 | yellow-orange | 1+2/3 | Performs like #15, but more so. Longpass filter blocking visible wavelengths below about 520 nm | |
| 18A | visually opaque | Based on Wood's glass, transmits small bands of ultraviolet radiation and infrared radiation. | ||
| 18B | very deep violet | Similar to 18A but with wider bands of transmittance in both the ultraviolet and infrared, a less 'pure' filter. | ||
| 21 | orange | 2 | Contrast filter for blue and blue-green absorption. Longpass filter blocking visible wavelengths below 530 nm | |
| 22 | deep orange | 2+1/3 | Contrast filter, greater effect than #21. Longpass filter blocking visible wavelengths below 550 nm | |
| 23A | light red | Longpass filter blocking visible wavelengths below 550 nm | ||
| 24 | red | Used for color separation of Kodachrome transparency film, complements #47B and #61. Longpass filter blocking visible wavelengths below 575nm. Red for 'two color photography' (daylight or tungsten). White flame arc tri-color projection.[5] | ||
| 25 | red tricolor | A | 3 | Used for color separation and infrared photography. Longpass filter blocking below 580 nm |
| 26 | red | Longpass filter blocking below 585 nm | ||
| 29 | deep red | F | 4 | 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. Longpass filter blocking below 600 nm. |
| 32 | magenta | Minus-green. Complements #12 minus-blue and #44A minus-red | ||
| 33 | magenta | Contrast filter for strongest green absorption. For photomechanical color masking | ||
| 34 | Indigo | |||
| 34A | violet | Used for minus-green and plus-blue separation | ||
| 35 | Navy | |||
| 38A | blue | Absorbs red, some UV, and some green light | ||
| 40 | light green | Green, for 'two color photography' (tungsten). | ||
| 44 | light blue-green | Minus-red filter with substantial UV absorption | ||
| 44A | light blue-green | Minus-red. Complements #12 minus-blue, and #32 minus-green | ||
| 47 | blue tricolor | C5 | Used for color separation. Complements #29 and #61 | |
| 47A | light blue | By removing much 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.[6] | ||
| 50 | deep blue | |||
| 56 | light green | |||
| 57 | green | Green for daylight 'two color photography'. | ||
| 58 | green tricolor | B | Color separation. | |
| 60 | green | Green for 'two color photography' (tungsten). | ||
| 61 | deep green tricolor | N | Color separation, complements #29 and #47. | |
| 70 | red | Used for color separation and infrared photography longpass filter blocking below 650 nm. | ||
| 74 | dark green monochromat | Transmits 10% of green radiation and virtually no yellow radiation from mercury-vapor illumination.[4] | ||
| 80A | blue | 4 | 2 | Raises the scene's color temperature from 3200 °K to approximately 5500 °K, which allows use of daylight balanced film with tungsten lighting. |
| 80B | blue | 3 | 1+2/3 | Similar to 80A; 3400 °K→5500 °K. |
| 80C | blue | 2 | 1 | Similar to 80A; 3800 °K→5500 °K. Typically used so that old-style flashbulbs cold be used on a daylight film. |
| 80D | blue | 1.5 | 1/3 | Similar to 80A; 4200 °K→5500 °K. |
| 81A | pale orange | 1.4 | 1/3 | Warming filter to decrease the color temperature slightly. Can be used when shooting with type B film balanced for tungsten lighting (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. The 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 °K) 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→3200 °K. |
| 85C | amber | 1.5 | Similar to 85; converts 5500 °K→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 °K) 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. | ||
| 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 °K) 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 °K) 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 740 nm | ||
| 87A | opaque | Passes infrared but not visible frequencies. Blocks wavelengths below 880 nm | ||
| 87B | opaque | Passes infrared, blocks visible frequencies. Blocks wavelengths below 820 nm | ||
| 87C | opaque | Passes infrared, blocks visible frequencies. Blocks wavelengths below 790 nm | ||
| 88 | opaque | Passes infrared, blocks visible wavelengths below 700 nm. | ||
| 88A | opaque | Passes infrared, blocks visible wavelengths below 720 nm. | ||
| 89B | near-opaque red | R72 | Passes infrared, longpass filter blocking visible wavelengths below 690 nm (very deep red). Aerial photography is one use. | |
| 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. Longpass filter blocking visible wavelengths below 625 nm | ||
| 93 | green | Color densitometry. | ||
| 94 | blue | Color densitometry. | ||
| 96 | gray | varies | Neutral density filter. Blocks all frequencies of visible light approximately evenly, making scene darker overall. Available in many different values, distinguished by optical density or by filter factor. | |
| 98 | blue | Like a #47B plus a #2B filter. | ||
| 99 | green | Like a #61 plus a #16 filter. | ||
| 102 | yellow-green | Color conversion for photometry: Makes a barrier-level type photocell respond as a human eye would. | ||
| 106 | amber | Color conversion for photometry: Makes a type S-4 photocell respond as a human eye would. |
See also
- Filter factor
- Filter (photography)
- Filter (optics)
References
- "Kodak Wratten numbered filters offered by Tiffen". Tiffen.
- "Kodak Wratten filters for black & white photomicrography". FSU Micro Magnet. Florida State University.
- "Wratten filter codes and uses". RedisonEllis.com.
- Peed, Allie C. Jr., ed. (n.d.). "Transmission of Wratten Filters". Handbook of Kodak Photographic Filters (PDF) (Report). Eastman Kodak Co. p. 127. ISBN 0-87985-658-0. Pub B-3, Cat 1528108 – via karmalimbo.com.
- Kodak Wratten Filters (4th ed.). London, UK: Kodak Ltd. 1969.
- Sawicki, Mark (1 June 2007). Filming the Fantastic. Focal Press. ISMB 0240809157 – via Google Books.
External links
- Wratten Light Filters (Google ebook edition) (4th ed.). Eastman Kodak Company. 1920 – Gives graphical spectral transmission curves for all Wratten filters available as of the publication date.
- Peed, Allie C., Jr., ed. (n.d.). Transmission of Wratten filters (PDF) (Report). Eastman Kodak Company. Retrieved 2020-08-08 – Detailed compilation of numerical information on spectral transmission of Wratten filters, reproduced in the 90th CRC Handbook.
- "Kodak Professional Accessories" (PDF) (catalog). Tiffen.
- "Filters". filmcentre.co.uk. FAQs for DPs.
- "Color correction filters table". GeoCities. Cokin Filter System. Archived from the original on 2009-10-28.
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