exposure
Measuring light
To calculate correct exposure the intensity or level of light has to be measured. Light is measured
by a light meter. Understanding the types of metering used in most cameras is an important skill.
All light meters inform the photographer of the amount of light available to obtain an appropriate
exposure. This information can be used to set aperture and shutter speed settings in a variety of
combinations. Each combination will give different visual outcomes whilst retaining the same overall
exposure (depth of fi eld and motion blur). Working in a creative medium such as photography
‘correct exposure’ can sometimes be a very subjective opinion. The photographer may want the
image to appear dark or light to create a specifi c mood.
Appropriate exposure
A light meter reading should only be viewed as a guide to exposure. Digital image sensors are
unable to record the broad range of tones visible to the human eye. If the camera frames a subject
with highlights and shadows the image sensor may only be able to capture the highlight tones or
the shadow tones, not both. An extremely bright tone and an extremely dark tone cannot both
record with detail and texture in the same framed image. Underexposure and overexposure in one
image is therefore not only possible but common.
It is often necessary for the photographer to take more than one reading to decide on the
most appropriate exposure. If a reading is taken of a highlight area the resulting exposure may
underexpose the shadows. If a reading is taken of the shadows the resulting exposure may
overexpose the highlights. The photographer must therefore decide whether highlight or shadow
detail is the priority, change the lighting or reach a compromise. A clear understanding of exposure
is essential if the photographer is to make an informed decision.
Exposing for highlights - Mark Galer