Modern digital cameras have the ability to evaluate and adjust the brightness of a subject all on their own. The exposure recommendation displayed in the bottom of the viewfinder and on the LCD are the cameras meter or brightness measurement of the scene. On the inside of your camera next to the image sensor is a metering sensor that measures the light values passing through the lens.
By default, your camera is most likely set to use an evaluative or matrix type metering system. This is an advanced system that uses a huge library of luminescence patterns and algorithms to determine the appropriate brightness. Sometimes, however, the camera doesn’t do a good job. This usually happens when there are extreme dark or bright areas within the image. When this happens you should know how to use the other types of metering available. There are three main types of metering modes available on most cameras.
Matrix or evaluative metering
Matrix and evaluative metering mean the same thing. Which your camera uses will depend on manufacturer. This is the most advanced form of metering of the three. The image frame is divided into a grid and analyzed for light intensity and distribution. Information on distance, color, hue, saturation and luminance is all processed. The data is then compared to a huge library of illumination patterns that the camera has stored.
The camera then sets the metering to suit the subject and the background. Matrix type metering is ideal for almost all situations and is definitely where you should start if you’re a beginner. When matrix metering does fail to do a good job, it is usually because of extreme light or dark areas in the frame. When this becomes an issue it is often beneficial to use one of the other available modes.
Center weighted metering
On more basic point-and-shoot type cameras that don’t have an advanced form of metering, center weighted metering is the default. Of the three types, center weighted provides the most consistent results.
As the name implies, the center of the frame gets the most consideration. Although a luminescence reading is taken from the entire frame, a circular area in the middle of the frame provides about 60-80 percent of the data. The remaining 20-40 percent of the data is taken from the area outside the circle. The area of the circle usually makes up about 10-15 percent of the whole frame. Center weighted metering is especially helpful with subjects that have a brightly lit background that you don’t want to affect the exposure of the subject.
Partial or Spot metering
Partial or spot metering works on the same idea as center weighted metering in that it puts a priority on the center of the frame.
The difference is that spot metering uses a much smaller area and it does not take any information from outside the center. The total area usually consists from 1 to about 5 percent of the total frame. Spot metering is very accurate if you are only worried about metering a small part of the frame. It works very well for photos of brightly lit small objects.
Which mode is the best?
Each metering mode serves a specific purpose and the best mode will depend on the situation. The subject, ambient lighting and your own preference will all have an impact. Most of the time matrix metering will work just fine for your photographs. Images with high contrast will often benefit from center weighted metering. Spot metering is best when highlighting small objects and for dealing with bright backlighting.
The best way to learn is with lots of trial and error. If using one mode doesn’t work for you, try another. Get to know how your camera works in different situations and get out and try different combinations of exposure settings. That way when a once-in-a-lifetime opportunity arises, you’ll be prepared. Don’t forget that you can always adjust the exposure compensation to make up for slight exposure differences.