Color temperature is a means of measuring
the energy level of color and is expressed in degrees Kelvin (K).
Each color on the visible spectrum is assigned a Kelvin temperature or,
more accurately, a range of temperatures, so knowing the color
temperature of a light source at any one time gives us important
information about the quality of the light.
Some information on color temperature in
For color film, at the warm red end,
small shifts in color temperature will result in large changes in color
rendition on film. At the cool end, however, small shifts in color
temperature result in comparably less change in color rendition. Thus,
color films that are designed and balanced for daylight are able to
produce acceptably accurate color under a wide range of natural or
electronic-flash lighting conditions.
Films balanced for tungsten illumination
only respond and deliver acceptable results within a rather narrow band
of color temperatures. It is worth noting that the range of acceptable
color with tungsten film is far smaller than when using
daylight-balanced film under its designated light sources.
There are separate films made to be used
with 3200K and with 3400K.
Only one group of films is necessary to
cover the entire daylight spectrum from about 5000K to over 10,000K.
Although we have poor color memory, our
psychological tolerance for certain colors that do not appear natural
in a photo is very limited at best. Skin tones, blacks, whites, and
grays are critical hues in this regard.
Not only are color films balanced for
daylight or tungsten illumination, most individual films by brand are
made to favor a particular cast from warm (red, orange, and yellow)
through neutral, where colors appear more or less as we expect them to
look, to the cool end of the spectrum (colors ranging from neutral to
those with a bluish cast).
Film-makers go so far as to adjust color
dye ratios for different film batches intended for sale in different
parts of the world. Therefore, a film intended for the U.S. market
might reflect a discernibly different color balance than the same brand
and type sold in Europe or Asia.
What makes all this so difficult is the
concept that acceptable color is a purely subjective decision on the
part of each observer. For instance, what I consider pink, you might
very well perceive as red. There are no objective, universal colors
everyone agrees upon. There are only ones that a consensus points to
and says, "These are colors that most agree fit the arbitrary names we
have assigned to them." Thus, colors such as red, blue, green, or
purple are only psychologically acceptable and by no means absolute.
There are methods and tools at our disposal to modify the color balance
of film so that the images they produce exhibit acceptably natural
colors. Filtration is the primary color-altering technique. It should be noted
that even with perfect technical balance between film and light source,
visible color imbalances still occur when lenses are coated with
microscopically thin layers or coatings meant to contain aberrations,
increase light transmission, or improve contrast. The effect of lens
coatings on color balance and color rendition is variable even from
lens to lens within the same brand lineup. Be aware that hues become
contaminated by color reflected onto subjects from adjacent objects.
Large areas of painted walls reflecting light on any photographic
subject will invariably alter the overall color of the subject. If, for
instance, one photograph a subject dressed in a red sweater standing
near a yellow wall and the light from that wall reflects onto the
subject, then the red sweater is likely to be recorded on film not as a
pure red but as a somewhat orange, less intense hue.