Basic Concept: Exposure & Metering

The concept of "exposure" is vitally important in photography. I think that most readers should be familiar with it. In summary, exposure refers to the relative darkness or lightness of a picture. Imagine your TV and you either cranking up the brightness to max. The colors will look washed out and everything will look unnatural. The opposite extreme is under exposing where you reduce the brightness to the lowest possible level and everything looks muddy and dark. It is clear then that it is important to adjust the brightness on your TV to get the proper colors. These same concepts apply to photography.

A key thing that every camera does is metering. There are may different metering algorithms and methods and they will vary by manufacturer and camera model. In short metering, is the technology that camera uses to decide the appropriate exposure for the picture. This may seem simple in theory, but actually can get quite complex. Let me give an example:

You are taking a picture of a person standing in front of a bright background. The situation assumes that the background is much brighter than the person. If the camera were to meter on the background, then the person would end up being dark and the background would be exposed properly. Alternatively, if the camera metered on the person, the person would be properly exposed and the background would be over exposed.

In both scenarios above, the camera is behaving properly. It is simply exposing for the image or portion thereof that is presented. This is then the challenge of metering. The actual process of metering is relatively straightforward, that is, it is not that hard to decide the appropriate exposure level. The issue is deciding what to meter on. In our example above, the question is should you expose on the background, the person or perhaps something totally different. Unfortunately, this is often more of a question of art than science.

The big difference between Digital SLRs and Point and Shoots cameras is that you can easily adjust metering and exposure settings in the dSLR while in most P&S’s, the decisions are left up to the camera which may not make the right choice.

In upcoming posts, we will talk more about exposure and what are the common ways to change it by adjusting camera settings.

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