optical density

Definition: (1) Measure of light-stopping or dispersing power of a transmitting material. * It is equal to the logarithm of the ratio of the illuminance of the incident to the illuminance of the transmitted light. (2) Measure of light-reflecting or dispersing power of a reflective material. * It is equal to the logarithm of the ratio of the illuminance of the incident to the illuminance of the reflected light. * In photography, density is usually normalised to a base density of zero. * In both senses: may be referred to simply as density. All of life in four units Photographically speaking, all of life gets crammed into four little density units: for that is about as much as any photographic system can handle and therefore all that we ever see or work with as photographers. In practice we're talking about a range of about twelve stops or more like ten or eleven. That is enough to express all the subtlety of tones, the glory of colour and richness of life. It's poetry, that's what it is.

Previous Term: optical contact  Next Term: optical distance