Basics 1: Exposure

Exposure is the fundamental building block of photography. We need to see what we we have photographed in order to have any discussion about the various controls and settings or to make any judgement on the quality or artistic merits of the image. Exposure describes how bright or dark a photo appears. Originally it depended on how much light film was exposed to. More Light = More Exposure = A Brighter Image. With digital cameras, that concept still applies; we’ve replaced the film with an electronic sensor.

“Correct” exposure is very subjective, based on the artisitic goals of the photographer. We’ll save that for a later article.

We can control exposure several ways. Inside the camera, the 3 primary controls are Aperture, Shutter Speed, and ISO. Outside the camera we can control exposure by controlling the environment. The environment contains some amount of light available to capture. The camera governs how much of that light reaches the film or sensor and how the camera processes it.

The Exposure Triangle is a helpful tool to understand the balance of the controls that affect exposure. Adjusting any one of the elements will adjust final result. Aperture controls how wide the shutter opens to let in light, like a curtain on window. Open the curtain more, and more light comes in. Shutter Speed controls how long the shutter is open. The longer the shutter is open, the more light enters, and we get a brigher image. In the simplest terms, ISO controls how sensitive the camera is to light.

The images below demonstrate the effects of Aperture, shutter speed, and lighting levels. ISO is constant in these examples (100). The center picture is our base exposure. Top left is greatly over-exposed and the bottom right is greatly under-exposed. Aperture settings go from more open on the left (f/5.6) to more closed on the right (f/22). Shutter speed settings decrease from slower speeds at the top (0.3s) to faster speeds at the bottom (1/50s). To see the effect of lighting, the second page of images use the same exposure settings, but reduce light by half.

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