The light meter in cameras has changed a lot over the years. They have progressed from "center-weighted " metering to cameras with "matrix"(also known as multi-segmented) metering. The "center-weighted" metering averaged the entire scene giving extra emphasis on the central portion of the viewing image. Multi-segmented metering divided up the viewing area into "pieces" like a jigsaw puzzle and used complex algorithms to determine the best exposure. Nikon took this one step further with the F5 which had 1005 pixels which used color to help determine the best exposure. The majority of the time, the meter will come up with an acceptable exposure. There are however, situations where even the most advanced meter will fail. One way to deal with this problem is to set your camera to "manual exposure". In this mode, you set the shutter and aperture values.

This month we will discuss using the "manual" exposure mode on your camera. Most modern cameras offer a variety of metering modes such as aperture-priority, shutter priority, programmed modes as well as manual mode. In all modes, except manual, the camera decides and sets the exposure for you. There are a few circumstances where manual mode is preferred.

An important item to remember is that as long as the light falling on your subject stays the same, the exposure for it will be the same regardless of how the foreground or background changes. For example, consider the photograph of the swimming merganser. The bird is in the surf, which means that, every few seconds the surf "crashes" creating a bright white area in the frame. This bright area will trick your light meter into underexposing. A way to deal with this is to meter your subject when there are no bright (or large dark areas) and set the shutter and aperture manually. Thus when bright areas appear, the camera will not underexpose.

Photographing birds on bright snow is problematic. The snow will cause underexposure of your photograph. One way to deal with this situation, is to manually set your exposure by metering an area of neutral tones. Tree trunks and evergreens will often suffice. Use this reading to determine your aperture and shutter speed, then re-compose and shoot. Be careful that the light falling on your subject is the same as the light falling on your metering area.

In summary, setting the exposure manually will compensate for unusually bright and dark areas that would otherwise cause exposure problems. You must however, remain conscious of the light conditions as they can change dramatically simply by having a cloud move across the sun. As usual, when the exposure situation is in question, be sure to bracket your exposures. Subtle differences in tone between your chosen metering area and subject may not be obvious and can adversely affect the final image.