Wratten number

They are named for the founder of the first photography company, British inventor Frederick Wratten.

[1] The numbering scheme can be divided into broad categories by use including color, monochromats, photometrics, and miscellaneous.

[3]: 16–19 Wratten filters are often used in observational astronomy by amateur astronomers.

Many manufacturers make filters labeled as 81B with transmission curves which are similar, but not identical, to the Kodak Wratten 81B.

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.

Thus, it has become difficult to find Wratten filters in photography stores.

For instance, some sets were for commercial photographers to adjust contrast in black-and-white photography with orthochromatic and panchromatic films.

[3]: 7 The Wratten filters numbered with 80, 81, 82, and 85x are color conversion filters used to avoid unnatural colour casts when photographing scenes where the color temperature of the light source does not match the rated color temperature of the film, which is available in Tungsten and Daylight types.

The shift is the difference in the mired values of the film and light source.

Likewise, when the film has a lower color temperature than the light source, a positive mired shift is required, which calls for an amber "warming" filter.

[10]: 58–59 [11]: 7  A typical set of color conversion filters has a geometric sequence, e.g. ±15, ±30, ±60, and ±120 mired,[9]: 41  which approximates the sequence established by the Wratten filters, and allows intermediate values to be obtained by stacking.