Exposure is the act of making film available to light so that an image is formed in the emulsion. The scene’s lighting–natural or set up–and the length of time exposed to light determines the exposure in a shot. Film that is overexposed, which occurs when the film has been exposed to light for an extended period of time, tends to have a bleached-out look; conversely, underexposed film looks dark. The effect of the dream sequence at the start of Ingmar Bergman’s Wild Strawberries (1957) is achieved through overexposure, the nature of the film stock, and laboratory processing.
Unless a particular aesthetic affect is intended, film is exposed to a level at which there will be a clear image that is consistent throughout the film. A light meter is frequently used to calculate the f-stop number. Specifically, the meter measures either incident light or the light reflecting off a subject and calculates the number. In addition to the f-stop, the t-top calculates the transmission of light. An exposure calculator can be used to determine the exposure setting as well. Finally, camera speed and film emulsion can also determine exposure.