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Understanding your camera's exposure function

Created date

June 29th, 2015
b/w photo with exposure
b/w photo with exposure

Every photograph is created using three functions of the camera working together—aperture, shutter speed, and ISO. This trio is known as the exposure triangle, or simply, exposure. Most every digital camera can adjust these functions automatically. If you prefer to manually adjust exposure, it is important to understand the role that each performs and the relationship between them. 

The lens aperture determines how much light gets through the lens to the camera sensor or film. Most lenses have a mechanical diaphragm that can be adjusted to let in a greater or lesser amount of light. Some small cameras do not have a diaphragm. Light falling on the sensor of these cameras is adjusted electronically by an automatic neutral density filter. 

The camera’s shutter determines how long the light coming through the lens remains on the sensor. Some cameras use a mechanical shutter.  Some do this electronically. Some use both.

The remaining component of the exposure triangle, ISO (named for the International Organization of Standardization), refers to the light sensitivity of the sensor. ISO can be regulated automatically by the camera or manually set by the photographer. Non-digital cameras use rolls of film that are rated at different levels of sensitivity—ISO 100, ISO 400, and so on—the higher the number, the more sensitive the film.

The trio at work

These three functions then, working together, are necessary to get a properly exposed photo, one that is of sufficient brightness and with accurate colors. Your camera can regulate exposure automatically and, in most instances, produce excellent photos. Even in special circumstances when you set your camera to a “scene” mode, the camera automatically adjusts the components of exposure to get an accurately exposed picture for that condition.

Photographers who use cameras with manual controls can choose to set these functions separately. Or, they can just set one member of the trio, say the aperture, and let the camera automatically choose the shutter speed and ISO. 

The key thing to understand is that proper exposure, made up of the three components of the photographic process (aperture, shutter speed, and ISO), is always necessary for a good photo.