Exposure compensation
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Exposure compensation is a technique to compensate a measured exposure level against other factors which may render a less-optimal image. This may include variations within a camera system, filters, non-standard processing, or intended under or overexposure. Cinematographers may also apply exposure compensation for changes in shutter angle or film speed, among other factors. In photography, some cameras include this as a feature to allow the user to adjust the automatically calculated exposure. Compensation can be applied both positively (additional exposure) and negatively (reduced exposure) in steps, normally in third or half F-stop increments up to a maximum of normally two or three stops in either direction.
Exposure compensation is employed when the user knows that the camera's automatic exposure calculations will result in an undesirable exposure. A scene that is predominantly light tones will often be underexposed, while a dark-toned scene will be overexposed. An experienced photographer will have gained a sense of when this will happen and how much compensation to apply to get a perfectly exposed photograph.