COLOUR COMPENSATING FILTERS
Contrary to the 80 Series filters (blue or orange) which are designed to rectify prevailing chromatic tints coming from the differences in colour temperature between the film and that of the light source(s), the colour compensating filters (cyan, magenta and yellow) correct dominant monochromatic colours, linked to various causes, from intrusive re•ections/glare/undesired rays to reciprocity failure. Originated from the famous Kodak® Wratten gels, the COKIN CC filters are equivalent to them chromatically, but have proven to be much more rugged/resistant in the long term. Working on the principle of subtractive syntheses of colours, these filters – each available in 6 different intensities that can be combined as necessary – allow for correction of any chromatic discrepancy.

Their uses are numerous and varied : balancing a mixture of light sources, compensating an aging flash tube, rectifying the occurrence of intrusive reflections/glare/an undesired ray, correcting the colour discrepancy in B mode that comes from reciprocity failure, removing the chromatic variation of certain films, etc. Their use is a matter of experience and attention, check of the film manufacturers’ instructions, knowledge of the light sources, and – with the latter – the use of a three-channel colour meter, such as the Minolta® III F, which measures ambient colour temperature and works directly with the CC filters.
Photo : Ariel Greco
Besides these purely technical uses (that often come up in commercial, industrial, or architecture photography),
these filters can also play a very interesting creative role by introducing a dominant colour, subtle or pronounced, according to the type of filter used. One can also discreetly emphasize the tint of certain pale subjects with a filter of density 05 or 10 in the appropriate colour.
These filters let blue, green and cyan tones pass but block(absorbs) red.

CC 05C : cyan density 5 + around 0 stop
CC 10C : cyan density 10 + around 1/3 stop
CC 20C : cyan density 20 + around 1/3 stop
CC 30C : cyan density 30 + around 1/3 stop
CC 40C : cyan density 40 + around 2/3 stop
CC 50C : cyan density 50 + around 2/3 stop
These filters let red, blue and magenta tones pass but block(absorbs) greens.

CC 05M : magenta density 5 + around 0 stop
CC 10M : magenta density 10 + around 1/3 stop
CC 20M : magenta density 20 + around 1/3 stop
CC 30M : magenta density 30 + around 2/3 stop
CC 40M : magenta density 40 + around 2/3 stop
CC 50M : magenta density 50 + around 1 stop
These filters let red, green and yellow tones pass but block(absorbs) blues.

CC 05Y : yellow density 5 + around 0 stop
CC 10Y : yellow density 10 + around 0 stop
CC 20Y : yellow density 20 + around 1/3 stop
CC 30Y : yellow density 30 + around 1/3 stop
CC 40Y : yellow density 40 + around 1/3 stop
CC 50Y : yellow density 50 + around 1/3 stop
NOTE : With digital shooting, the use of these filters is still relevant, as much for the simplicity and time gain that they bring in practice, as for the sureness and predictability of their results.
Yes, an automatic white balance can work well, but in the large majority of difficult situations, good filtering during the shooting remains and will always be preferable. One can certainly attempt to apply the same correction to the image during post-processing, but the time spent will not be the same, by far! And you must still know how and be able to do it, for you risk not being able to correct the dominant unwanted tints, because in this case you must add colours.