An understanding of exposure is critical for the photographic process

Exposure

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 (MIE) 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 is the action of subjecting a light-sensitive medium to light. Lenses and cameras control how much light (aperture) and how long the light (time) is 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 - amount and duration.

Too much light will result in overexposure. Too little light will result in underexposure. It makes no difference whether there is very bright or a very dim level 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 amount (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.

Using a higher ISO setting in the camera means the camera will need less light to make an exposure but also has the effect of lowering the quality of the image by introducing ‘noise’ (noise in an image can be likened to film grain or interference on a TV). This noise leads to a loss of smooth tone in a digital image that becomes more noticeable the larger the image is printed or magnified on screen.