essential skills: digital photography in available light
Introduction
An understanding of exposure is without doubt the most critical part of the photographic process.
Automatic exposure systems found in many sophisticated camera systems calculate and set the
exposure for the photographer. This may lead some individuals to think there is only one correct
exposure, when in reality there may be several. The exposure indicated by an automatic system,
no matter how sophisticated, is an average. Creative photographers use the meter’s indicated
exposure reading for guidance only. Other photographers may interpret the same reading in
different ways to create different images. It is essential the photographer understands how the
illuminated subject is translated by exposure into a photographic image.
Exposure
Exposure is the action of subjecting a light-sensitive medium to light. Cameras and lenses control
the intensity of light (aperture) and the duration of light (time) allowed to reach the image sensor.
The intensity of light is determined by the size of the aperture in the lens and the duration of light
is determined by the shutter.
Exposure is controlled by aperture and time - intensity and duration.Too much light will result in overexposure. Too little light will result in underexposure. It makes no
difference whether there is a large or a small amount of light, the image sensor still requires the
same amount of light for an appropriate exposure at any given ISO setting.
Exposure must be adjusted to compensate for these changes in the brightness of the available
light. This is achieved by adjusting either the intensity (aperture) or duration of light (time) or
by adjusting the ISO on the camera. Increasing the size of the aperture gives more exposure,
decreasing gives less. Decreasing the duration of the shutter speed reduces exposure, increasing
gives more. Changing the ISO on the camera adjusts the sensitivity of the image sensor to the
available light.
Overexposure Correct exposure Underexposure