Camera Metering

by Mike Schumacher

Along with exposure compensation and stops of light, your camera metering mode will also affect how the camera interprets the light levels in a scene. There are 4 basic types of metering.

Multi zone metering takes in the whole scene. Depending on the camera it might be called matrix, evaluative or multi zone, but it basically involves sampling multiple areas in a scene and using that to determine an f-stop and shutter speed.

Center Weighted metering averages the whole scene with emphasis on the center of the scene.

Partial metering meters only the center of a scene, usually about 9% of center.

Spot metering meters only the center usually about 1 -> 3%.

Which of these metering systems you have will depend on the camera. Most will have multi zone, center weighted and partial or spot.

When your camera meters a scene it is calibrated to expose for middle gray or about 18% gray. The problem with this can be over or under exposure at extreme light levels. A dark scene will be brightened to 18% or over exposed and likewise a bright scene will be darkened to 18% or underexposed.

Modern cameras do a fairly good job on most scenes in the multi zone mode. It's extremes of light where we have problems. If you have a scene where a certain portion is brighter of darker that the rest and that's what you want to expose for you can use center weighted, take a reading and re-compose.

If you are shooting flowers you might want to use partial or spot. Bracketing exposures comes in handy for tricky lighting. The camera will automatically bracket + 1/3 or ½ and – 1/3 or ½ depending on your settings. A bracketed set is usually 3 exposures. One at the recommended setting and one above and one below. You can also use exposure compensation and do it manually. If you have a very bright scene with some deep shadows you will have to decide what you are exposing for. Take a spot or partial reading on the bright or dark areas and use exposure compensation accordingly.

For a dark area you would use minus exposure compensation and for bright areas you would use plus exposure compensation. Start with 1/3 or ½ stop and expose multiple frames. This sounds backwards but remember that 18% middle gray?

The whole point of this is your cameras meter can be fooled. It can and will expose a scene with difficult lighting wrong. This is why a scene with a lot of white like a snow scene with very little else will turn gray unless you use plus exposure compensation.