Metering Mode - What is it, and how does it affect my photos?

Metering Mode - The method your camera uses to measure available light and make an assessment as to Aperature and/or Shutter Speed for each exposure.

Many high end cameras allow you to select from several different metering modes. Depending on which mode you choose, your pictures may or may not come out the way you expected.

Example modes are as follows:

Spot Metering - Uses a very small amount of the scene (as shown through the viewfinder) in the very center of the image.

Center Weighted - Uses a larger area out of the center of your scene, and then averages the remainder of the scene.

Average Weighted - Uses the entire scene.

There are other methods not listed here, and some manufacturers may use terms slightly different than these. In each method, the camera is taking a Reflective Meter reading from the scene, and the only real difference between the methods is how much of the scene to use and what weight to give different parts of the scene.

By "reflective meter reading", I mean that the camera actually measures the amount of light being reflected from your subject and/or scene back through the lens of the camera. The reflective characteristics of different parts of your scene can have a dramatic impact on the final image and whether or not your camera guesses right about how much light is really in the scene.

As an example, imagine two photographs taken at the same time of the day in the same area outside your home. It's a sunny day, and your subjects (let's say your son and your daughter) are sitting on a chair facing the sun. You are standing in front of them with the sun at your back. Your son is wearing his favorite AC/DC concert t-shirt which is pure black. Your daughter is wearing a white lace tank top. If you are using Spot Metering and point your camera at their body, in one case your photo will come out over-exposed, and in the other it will come out under-exposed. That's because the light sample is being taken from a very small area of the scene around the middle of the viewfinder. In this example, it might be better to take your reading from the entire scene instead, and so you would use Average Weighted for more consistent results from shot to shot.

On the other hand let's say that you are taking a picture of your daughter with her back to the sun (i.e. you are shooting into the sun). This might be a better use for Spot Metering so that you get a good reading on the light coming from your subject's body, and not the very bright light coming from behind in this back-lit situation. Of course the area around your subject will probably be over-exposed, but at least your main area of concern (your daughter) will be properly exposed.