Exposure is a photography term that has several meanings. For our purposes here, it refers to the Shutter Speed, Aperture and ISO sensitivity camera settings used to create an image. Photography is a process of capturing light to create an image. The three settings that form the exposure triangle control light gathered by the lens in different ways. A correct exposure is any combination of settings that results in an image that is neither too light nor too dark. Ideally, this image would retain details in the brightest and darkest tones with no area being featureless white or black.

A simple way to visualize how it works think of light as if it were water. Creating a correct exposure is like filling  a container with water until it’s exactly full. Too much water and the container overflows; the image is over exposed (too bright). Too little and the image is underexposed (too dark). The length of time that the water is on, represents the shutter speed. The aperture is like controlling the flow of the water. The ISO is akin to the size of the container.

Filling a small container (high ISO) with the faucet completely open (wide aperture) will take very little time (shutter speed).  If the container is made to be twice as large, the water must flow twice as fast or for twice as long to fill it. This is how a camera works as well. Each increment of a given setting is called a stop. If one increases a particular setting by a stop, one must decrease one of the other settings by an equivalent stop to maintain a correct exposure. Each stop allows twice as much light as the previous and half as much as the next.

Any combination that results in an image that has exactly enough light is a “correct exposure” each combination will create an image with different qualities and require different trade-offs.  Those will be discussed in upcoming  articles.