filter factor

A filter factor is a number used in photography to adjust exposure time when using a color filter. This adjustment is necessary because filters absorb some light, altering the exposure needed for a correct image. The filter factor indicates how much the normal exposure time must be multiplied to compensate for the light loss caused by the filter and the specific lighting conditions.12

Filters themselves are devices, often made of colored glass, plastic, or gelatin, placed over a camera lens or light source. They selectively modify the wavelengths of light before they reach the film. In black-and-white photography, they help translate colors into appropriate gray tones and control contrast. In color photography, they adjust the light's quality to match the film's sensitivity. Neutral density filters reduce light intensity without changing color, while polarizing filters reduce glare and enhance color saturation.2