Wratten number

From Wikipedia, the free encyclopedia

Wratten numbers are a labeling system for optical filters, usually for photographic use.

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 continued to produce "Wratten Filters" for decades. Even now, as of 2006, Wratten filters are still produced by Kodak, and sold under license through the Tiffen corporation.

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 which do similar but not exactly the same filtering of light, 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 for printing press color separation or scientific photography tend to have less variation.

[edit] Reference Table

The commonly available numbers and some of their uses include:

Wratten number	Color	Filter factor	Uses and characteristics
1A			Called a skylight filter, this absorbs ultraviolet radiation, which reduces haze in outdoor landscape photography.
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.
4	yellow
6	light yellow
8	yellow	2	Absorbs more blue than #3.
9	deep yellow		Absorbs more blue than #8.
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 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.
15	deep yellow		Darkens the sky in black and white outdoor photography.
16	yellow-orange		Like #15, but more so.
21	orange		Contrast filter for blue and blue-green absorption.
22	deep orange		Contrast filter, greater effect than #21.
23	light red
24	red
25	red tricolor		Used for color separation and infrared photography.
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.
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		Color separation.
50	deep blue
56	light green
58	green tricolor		Color separation. By removing light that isn't green, green objects like foliage show a broader range of colors.
61	deep green tricolor		Color separation, complements #29 and #47.
80A	blue	4	Color Conversion. Raises the color temperature, 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	Similar to 80A; 3400 K to 5500 K.
80C	blue	2	Similar to 80A; 3800 K to 5500 K. Typically used so that old-style flashbulbs can be used on a daylight film.
80D	blue	1.5	Similar to 80A; 4200 K to 5500 K.
81A	pale orange	1.4	Warming filter to increase 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	Warming filter, slightly stronger than 81A. The opposite of 82B.
81C	pale orange	1.5	Warming filter, slightly stronger than 81B, opposite of 82C.
81D	pale orange		Warming filter, slightly stronger than 81C.
81EF	pale orange		Warming filter, stronger than 81D.
82A	pale blue	1.3	Cooling filter to decrease the color temperature slightly. The opposite of 81A.
82B	pale blue	1.4	Cooling filter, slightly stronger than 82A and opposite of 81B. Can also be used when shooting tungsten type B film (3200 K) with household 100W electric bulbs (2900 K).
82C	pale blue	1.5	Cooling filter, slightly stronger than 82B and opposite of 81C.
85	amber	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 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.
85B	amber	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) 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 kelvin) 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 kelvin) 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
87C	opaque		Passes infrared but not visible frequencies.
89B	near-opaque		Passes infrared, blocks visible wavelengths below 720 nm (very dark red). Aerial photography is one use.
90	dark grayish amber		Used for viewing scenes without color before photographing them.
92	red		color densitometry.
96	grayish	varies	neutral density filter. Blocks all frequencies of light 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; 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.