groping in the dark

Finding the right shade of gray

Previous entries have focused on the tools your camera gives you to achieve a good exposure. So but how do you know what the proper exposure should be? First, you need to know how much light you have to work with. Then you need to decide how to use that light to its best advantage.

Professional photographers sometimes use a light meter to actually measure the available light in a scene. This gives them a clue where to start with their camera settings. We beginning photographers can use the light meter that's built into our camera, in what is called through-the-lens (TTL) metering. When your camera is in auto-mode, it is this meter that determines the aperture and shutter speed. This is also where the default numbers that you see in your viewfinder for shutter speed and aperture come from. The in-camera meter measures the amount of light coming into the camera and assumes that the scene is reflecting 18% of the available light. A typical scene contains a fairly even mix of light and dark tones and the meter's assumption is based on the average of these tones. The range of these tones includes highlights (light areas), shadows (dark areas), and mid-tones (the middle values, i.e. grays).

Usually, your camera's TTL meter does a pretty good job of setting the exposure for most scenes, and you can use the readings as a good starting point for your manual exposures. Just remember that your meter is shooting for an average and not every scene contains an "average" range of tones. If you were to take a picture of a winter scene filled with snow using your camera's default setting, you will end up with a picture of gray snow. A picture of a black cat sitting in a black leather chair will end up being the same blah gray using the camera's default. This blah gray(18%) is the "average" value that the camera's meter is trying to achieve.

The key to dealing with these situations is to over- or underexpose. In a snow scene, you want to intentionally overexpose the image to keep the white snow from moving into grey. You can adjust your exposure using either aperture or shutter settings. This shot of Sam was one full stop overrexposed. In hindsight, I could have probably gone one more stop.