Kodak Wratten filter 80A in its original packaging

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 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 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 often 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 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 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;[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
2B pale yellowAbsorbs ultraviolet radiation, slightly less than #2A (letters out-of-order). Longpass filter blocking wavelengths shorter than 395 nm. Used for high-altitude photography.
2A pale yellowAbsorbs ultraviolet radiation and heightens contrast of clouds against blue sky. Longpass filter blocking wavelengths shorter than 405 nm. Used for high-altitude photography.
2C Absorbs ultraviolet radiation. Longpass filter blocking wavelengths shorter than 390 nm. Used for high-altitude photography.
2E pale yellowAbsorbs ultraviolet radiation, slightly more than #2A. Longpass filter blocking wavelengths shorter than 415 nm. Used for high-altitude photography.
3 light yellowAbsorbs 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 shorter than 440 nm. Used for high-altitude photography, and in astronomy to mask achromatic lens color-fringing.
4 yellowMinus-violetLongpass filter blocking visible wavelengths shorter than 455 nm. Used for high-altitude photography, and in astronomy to mask achromatic lens color-fringing.
6 light yellowK1Not a longpass filter
8 yellowK21Absorbs more blue than #3. Longpass filter blocking visible wavelengths shorter than 465 nm
9 deep yellowK3Absorbs more blue than #8. Longpass filter blocking visible wavelengths shorter than 470 nm
11 yellowish-greenX12Heightens contrast of skin tones in black & white photography. Not a longpass filter
12 deep yellowMinus-blue1+1/3Minus-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 shorter than 500 nm
13 green2Color enhancement. Not a long-pass filter
15 deep yellowG1+2/3Profoundly darkens the sky in black & white outdoor photography. Longpass filter blocking visible wavelengths shorter than 510 nm
16 yellow-orange1+2/3Performs like #15, but more so. Longpass filter blocking visible wavelengths shorter than about 520 nm
18A visually opaqueBased on Wood's glass, transmits small bands of ultraviolet radiation and infrared radiation. Used to block visible light from UV lamps.
18B very deep violetSimilar to 18A but with wider bands of transmittance in both the ultraviolet and infrared, a less 'pure' filter.
21 orangeYA32Contrast filter for blue and blue-green absorption. Longpass filter blocking visible wavelengths shorter than 530 nm
22 deep orange2+1/3Contrast filter, greater effect than #21. Longpass filter blocking visible wavelengths shorter than 550 nm
23A light redLongpass filter blocking visible wavelengths shorter than 550 nm
24 redUsed for color separation of Kodachrome transparency film, complements #47B and #61. Longpass filter blocking visible wavelengths shorter than 575 nm. Red for 'two color photography' (daylight or tungsten). White flame arc tri-color projection.[5]
25 red
tricolor		A3Used for color separation and infrared photography. Longpass filter blocking short of 580 nm
26 redLongpass filter blocking short of 585 nm
29 deep redF4Used 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 short of 600 nm.
32 magentaAMinus-green. Complements #12 minus-blue and #44A minus-red
33 magentaContrast filter for strongest green absorption. For photomechanical color masking
34 Indigo
34A violetUsed for minus-green and plus-blue separation
35 Navy
38A blueAbsorbs red, some UV, and some green light
40 light greenGreen, for 'two color photography' (tungsten).
44 light blue-greenMinus-red filter with substantial UV absorption
44A light blue-greenMinus-redComplements #12 minus-blue, and #32 minus-green
47 blue
tricolor		C5Used for color separation. Complements #29 and #61
47A light blueBy 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 greenGreen for daylight 'two color photography'.
58 green
tricolor		BColor separation.
60 greenGreen for 'two color photography' (tungsten).
61 deep green
tricolor		NColor separation, complements #29 and #47.
70 redUsed for color separation and infrared photography; longpass filter blocking short of 650 nm.
74 dark green
monochromat		Transmits 10% of green radiation and virtually no yellow radiation from mercury-vapor illumination.[4]
80A blue42Raises the scene's color temperature from 3200 K to approximately 5500 K, which allows use of daylight balanced film with tungsten lighting.
80B blue31+2/3Similar to 80A; 3400 K→5500 K.
80C blue21Similar to 80A; 3800 K→5500 K. Typically used so that old-style flashbulbs could be used on a daylight film.
80D blue1.51/3Similar to 80A; 4200 K→5500 K.
81A pale orange1.41/3Warming 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 orange1.41/3Warming filter, slightly stronger than 81A. The opposite of 82B.
81C pale orange1.51/3Warming filter, slightly stronger than 81B. The opposite of 82C.
81D pale orangeWarming filter, slightly stronger than 81C.
81EF pale orange1/3Warming filter, stronger than 81D.
82A pale blue1.31/3Cooling filter to increase the color temperature slightly. The opposite of 81A.
82B pale blue1.42/3Cooling 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 blue1.52/3Cooling filter, slightly stronger than 82B and opposite of 81C.
85 amber1.52/3Color 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 amber1.52/3Similar to 85; converts 5500 K→3200 K.
85C amber1.5Similar to 85; converts 5500 K→3800 K.
85N3 amberNeutral 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 amberNeutral 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 amberNeutral 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 opaquePasses infrared but not visible frequencies. Blocks wavelengths shorter than 740 nm
87A opaquePasses infrared but not visible frequencies. Blocks wavelengths shorter than 880 nm
87B opaquePasses infrared, blocks visible frequencies. Blocks wavelengths shorter than 820 nm
87C opaquePasses infrared, blocks visible frequencies. Blocks wavelengths shorter than 790 nm
88 opaquePasses infrared, blocks visible wavelengths shorter than 700 nm.
88A opaquePasses infrared, blocks visible wavelengths shorter than 720 nm.
89B near-opaque redR72Passes infrared, longpass filter blocking visible wavelengths shorter than 690 nm (very deep red). Aerial photography is one use.
90 dark grayish amberUsed for viewing scenes without color, before photographing them, in order to assess the brightness values. Not used for actual photography.
92 redColor densitometry. Longpass filter blocking visible wavelengths shorter than 625 nm
93 greenColor densitometry.
94 blueColor densitometry.
96 grayvariesNeutral 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 blueLike a #47B plus a #2B filter.
99 greenLike a #61 plus a #16 filter.
102 yellow-greenColor conversion for photometry: Makes a barrier-level type photocell respond as a human eye would.
106 amberColor conversion for photometry: Makes a type S‑4 photocell respond as a human eye would.

See also

References

  1. ↑ "Kodak Wratten numbered filters offered by Tiffen". Tiffen. Archived from the original on 2011-10-24. Retrieved 2011-09-29.
  2. ↑ "Kodak Wratten filters for black & white photomicrography". FSU Micro Magnet. Florida State University.
  3. ↑ "Wratten filter codes and uses". RedisonEllis.com.
  4. 1 2 Peed, Allie C., Jr., ed. (n.d.). "Transmission of Wratten filters" (PDF). Handbook of Kodak Photographic Filters (Report). Eastman Kodak Co. p. 127. ISBN 0-87985-658-0. Pub B‑3, Cat 1528108 – via karmalimbo.com.{{cite report}}: CS1 maint: multiple names: editors list (link)
  5. ↑ Kodak Wratten Filters (4th ed.). London, UK: Kodak Ltd. 1969.
  6. ↑ Sawicki, Mark (1 June 2007). Filming the Fantastic. Focal Press. ISBN 9780240809151. ISMB 0240809157 – via Google Books.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.