Tungsten Film

When we view common objects under different light sources, our vision makes subtle adjustments so that white appears white, black appears black, and other colors their expected hues, regardless of the light source. However, color photographic film has no such capability.
 

Most of us realize that tungsten lighting in the form of studio photo floods or ordinary house bulbs emit light rich in orange and red. The illumination produced by each of these sources is known as warm light. Contrasted to this, sunlight and electronic flash tubes give off light generically termed "daylight." This type of light is full-spectrum, but at certain times appears blue-rich and therefore cool. When taking pictures under specific light sources, color film must be matched to the light source to produce accurate hues. We can accomplish this in by either filtering the light to match the spectral response of the film or to match the spectral response of the color film to the light source.


Our eye adjusts for different light sources automatically. Film does not. For example, shooting with daylight-balanced film under tungsten lighting results in pictures displaying an overall orange cast. An orange color rendition might be perfectly all right and even desirable on some occasions, but usually it isn't. As stated earlier, we can use a filter to address the imbalance or switch to a film matched to the light.


Color film marked "daylight" is intended for use under natural daylight or electronic flash. Film labeled "tungsten" is normally employed for indoor situations where the principal light sources are either floods or other warm tungsten-light sources.


Indoor red-rich light has a low color temperature compared to blue-rich daylight. This seeming contradiction occurs because tungsten films designed for use with warm, red-rich lighting have smaller Kelvin numbers than cooler daylight films balanced for blue light. This situation is a constant source of confusion to many but we should understand the terms warm and cool are purely psychological descriptors, while the numerical designations of color temperature as expressed in degrees Kelvin are more correct scientifically.


Color film is most often used under compatible lighting. In order to provide photographers with color films that deliver realistic color under light other than daylight, major film suppliers make a number of color films, almost all of which are transparency materials whose color response is balanced for tungsten light. If you need to match color exactly, you will need a color temperature meter, an instrument that measures prevailing light and reads out its color temperature. After taking a color temperature reading, placing one or more special color-correction filters over either the light source or the taking lens should balance film and light source precisely.


At the cool end of the visible spectrum, color accuracy is a hit easier to achieve because large changes in color temperature do not result in as much of a color shift as at the lower end of the color temperature scale. Aware that color temperature meters and color compensating filters are both expensive and cumbersome, manufacturers make several slide films formulated to give normal color balance under several sources of tungsten light. There are a half-dozen such films that range from ISO 50 to 640. All but two are balanced for studio floodlights burning at 3200K. They are designated Tungsten Type A. One film, Kodachrome 40, balanced for infrequently used 3400K photolamps, is designated Tungsten Type B. Fuji has chosen to balance their tungsten films for a 3100K light source. They believe 3100K is closer to the actual color temperature of photo floods.


Tungsten film is useful under ordinary house lights although 60-150 watt bulbs burn at between 2300-2800K which is warmer (more orange) than photofloods. The resulting pictures will be warm but not always objectionably so. Tungsten film can be used in daylight with an 85B filter for a more normal color rendition.

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