Digital Camera Filters:
Color Filter in Photography

Filters are used to modify the characteristics of light in the photographic registration of a scene. We use them when the result we foresee before the shot doesn't correspond to the given scene and how we are seeing it or want it to appear.

The Filter Factor

All filters absorb a determined amount of light and are associated with a number, its factor, which indicates the necessary compensation in the exposure level to obtain an image of the correct density. A filter which reduced the intensity of the light in half, for example, is associated with a factor which can be expressed as -1 (increasing the exposure in one value) or as 2 x (multiplying the exposure level by two). The factor accompanies all filters, except those whose density is so light that it doesn't have noticeable absorption. The factor needs to be taken in account only when we measure the light with instruments that aren't affected by the filter. On the other hand, in reflex and digital cameras with through the lens measuring (TTL), the filter directly causes a decrease of measured brightness that, therefore, it taken in account automatically by the photometer.

Colored Filters

A colored filter or a transparent sheet of glass or gelatin has the effect of absorbing light of a determined color or type, modifying the characteristics of the beam of light that reaches the film. A color filter lets light pass or transmits the light in determined wavelengths and absorbs other colors (4.5). A filter that absorbs red and blue has a green aspect because it is the wavelength it transmits. A red or blue object photographed through a green filter will appear darker or black. The greater the tone's density , the stricter the choice of wavelengths. A filter has the purpose and an effect that depend on the type of film we are using. Therefore, we can subdivide colored filters in two categories: filters used for black and white emulsions, and those used with color emulsions.

Color Filters

In black and white we obtain a negative with different densities of gray; from the original negative and also through the developing (11.3) and printing (12.3). Also, there is no such thing as “fidelity” in black and white, because the disappearance of tones is a break with realism. The tones we obtain in a negative, with or without filters, aren't usually “objectively” questioned by the spectator, and the use of a filer is, except in extreme cases, undetectable. In color the problem is very different. There is a correct color balance , which we have defined as conditions were the neutral tones (grays) of the scene are reproduced as such in the photograph. These conditions are: 1) the color of the light that lightens the scene is of the same characteristics as the emulsion is balanced for (4.7.2 and 6.4); 2) that the exposure level doesn't pass the limits (4.8.3 and 4.9.3); 3) the exposure time isn't abnormally long or short (4.7.3). Any failure to fulfill the first or third of these conditions is going to cause a variation in the tones of the image with a predominance of a color ( dominant ). The strict color balance isn't a goal, but a starting concept . Through theory and experience we can foresee the image's colors; detect dominants and correct them when we anticipate they are going to be excessive; and finally, modify the colors in the sense we wish,, to reach the balance of abnormal conditions to alter the color balance at our will.

Digital Camera Filters: Color Filter in Photography

The Filter Factor

Colored Filters

Color Filters

Digital Camera Filters:
Color Filter in Photography