Filter the Light
Regardless of the media used to record the image, the most practical way to manipulate the color temperature is the physical filtering of light. Although it is possible to use glass filters or other rigid materials, for video production are used, in most cases, gelatin filters - thin films of polyester or acetate with a chromatic treatment that gives them a particular behavior.
The specific function of a filter is to transform, select or separate the different chromatic components of light. In extreme cases this represents radical changes in the color of the sources, but almost always the photographer's work concentrates on making subtle corrections aimed at giving the scenes a natural look, reconstructing the effects produced by the mixture of light sources of different quality.
The main tools for this work are conversion filters and color correction filters, which allow to precisely control the behavior of light sources and approximate the real processes of light mixing.
Color conversion filters
These filters fulfill the function of radically altering the color temperature of one light source to match that of others. Normally it is about manipulating light sources that vary between the color temperature of tungsten light (3200° K) and that of daylight (around 5600 ° K), although there are special filters for sources as peculiar as fluorescent light tubes or sodium lamps.
Typically, color conversion filters are used in lighting work when it is necessary to combine different light sources. For example, to mix artificial light of 3200°K with natural light of 5600°K it is necessary to use a blue gelatin filter, generally known as Color Temperature Blue.
If it is a question of achieving a mixture of color with a slight tendency towards one of the ends, graduated filters can be used, as described in the following table:
3,200°K + Full CTB = 5,600°K
3,200°K + 1/2 CTB = 4,350°K
3,200°K + 1/4 CTB = 3,775°K
3,200°K + 1/8 CTB = 3,487°K
Otherwise , Color Temperature Orange filters can be used, which reduce the dominant blue of daylight to be able to mix it with tungsten light and obtain the following results:
5,500°K + Full CTO = 3,200°K
5,500°K + 1/2 CTO = 4,350°K
5,500°K + 1/4 CTO = 4,925°K
5,500°K + 1/8 CTO = 5,212°K
The stability of the video results depends on the fact that at the beginning of the lighting process the correct white balance has been established for the reference light level, which must be the one that is intended to be achieved with the light filtering process. Equally important is the selection of the optical filter corresponding to the color temperature of the ambient light, which is equivalent to the color "balance" of each type of photographic emulsion.
Color correction filters
These filters, also called compensation, are of weaker colors and counteract slight differences in color temperature. They work on both the blue and red sides of the spectrum, which is why they are called "warm" or "cold" depending on the quality of their contribution to the mix of lights. The most commonly used compensation filters are as follows:
"Warm" "Cold"
(More Red) 85 (More Blue) 80A
85B 80B
81A 80C
(Less Red) 1A (SkyLight) (Less Blue) 82C
Although the above references correspond to camera filters, most manufacturers of gelatin filters offer equivalent versions that can be used to give small turns to the color of the lights. However, it is more frequent that, due to economic considerations, the videographer is forced to use low-intensity conversion filters to do correction work.
A good option in these cases is to use filters on the lenses, which can be used to give a continuous tone to a scene and attenuate the effects of a conversion filter.
Finally, let's remember that the control of the color of light is one of the main tools of the photographer, and that the success of creative work lies in the knowledge of the available tools. Do not forget that the best way to learn is to experiment and take note of every little detail that can one day become the key to a successful shot.
