Expose for Backlighting
A common film exposure problem is a backlit subject, or a subject standing in front of a lighter background or light source such as a window or the sun. Light meters, whether through-the lens or handheld light meter, are designed to meter averages in all tonal values of a particular scene. So when the subject is backlit by a lighter background or light source the meter will assume the entire scene is bright and sets an exposure that results in a darker image. Some photographers may hope to achieve a silhouette effect of the subject, in which case these results are fine, but many will hope to achieve an even, well exposed image.
To avoid silhouetting your subject against backlight, simply perform a light meter reading closer to the subject. With a built-in camera light meter, move closer to the subject so that most of the backlight is not within view, though you want to avoid blocking the light on the subject. While looking through the viewfinder of the camera focus on your subject until it just fills the viewfinder to take the reading. Then you can set your aperture and shutter speed accordingly, step back to your original position, refocus, and take the photograph. With a handheld light meter, again move as close to the subject as possible without blocking light. A spot meter, which measures a narrow angle of light, is particularly helpful for metering backlit subjects.
Silhouette the Subject with Backlighting
To achieve silhouetting, use the light meter to measure the entire scene and set the camera accordingly. It would be recommended to give a stop or two less exposure than your meter reads. This will allow for more contrast to capture the subject with a complete silhouette.
