The color qualities of color films are
matched to the same standard that governs the rating of the color
values of incandescent lamps and other similarly radiating light
sources. This color temperature - as it is called - is expressed in the
Kelvin temperature scale (˚K). Kelvin scale temperatures are equal to
the heat temperature of the radiating body in degrees centigrade, now
called Celsius (˚C), plus 273. Color temperature is basically defined
as a measure which defines the color of a light source relative to the
visual appearance of the light radiated by a theoretically perfect
radiator, or blackbody, heated to incandescence.
If a film is to be used with a light source for which it is not
balanced, it is necessary to do the needed color balancing on the film
through the use of filters. Color balancing filters for use with color
films have very specific color responses, and are made to be used with
only one basic color balance of light per film type.
Below are the types of filters being use commonly for color balancing:
Color Conversion Filters
Color conversion filters for color
balancing in photography is a group designed to take care of the common
gross changes that occur when a color transparency film is used with an
unsuitable light source.
There are three main types of spectral
balance in color slide films: Daylight-type, Type A, and Type B. Color
negative film can be assumed to be of Daylight sensitivity. If a Type A
or B color film is used in sunlight without a filter, the scene will
appear much too blue in the finished picture. A Color Conversion filter
is needed to assure a natural appearance in the final slide. And the
same is true of a Daylight-type film used with incandescent lighting,
except that without the filter the scene will appear too orange.
Light balancing filters is suitable for
situation where the degree of color imbalance is less extreme but still
in need of correction.
If the light source is nonstandard, it
can be brought into balance with the standard color films by using a
light-balancing filter of the 81 or 82 series. These are very pale
yellowish in color (the 81 series), or pale bluish (the 82 series). An
example of their use is where the light source was a desk lamp, rather
than a photoflood bulb.
Color Compensation Filters
In critical color photography there is frequently a need for great care
in balancing the light source to the film emulsion sensitivity as
exactly as possible. In order to do this, color compensation filters
(often called CC filters) are used. These come in six basic colors, and
in a wide variety of densities. The colors are cyan, magenta, yellow,
red, green, and blue. The first three are complementary to the second
three, in the order given. In terms of wavelengths of light absorption:
cyan absorbs red
red absorbs blue and green
magenta absorbs green
green absorbs blue and red
yellow absorbs blue
blue absorbs red and green
Color compensation filters are usually
seen in a series of standard calibrations. These run from .05 through
.50, with density and color saturation increasing as the number grows
larger. A color compensation filter of yellow color and a density of
.40 is called a CC40Y, and so on.