Ever wonder how your camera picks the right exposure (not too bright or too dark) for most of your shots? It’s because most cameras have built in light meters. The purpose of the meter is to measure the amount of light being reflected back into the camera from a particular subject or from a whole scene.
The camera then calculates the best shutter speed and aperture opening combination to yield a properly exposed image. (Or you set it yourself if you have the option of manual exposure settings.)
The light levels can vary from scene to scene or from subject to subject. So there are a few different ways meters can measure the light. The three most common are listed below.
Spot or Partial Metering
In this mode, the meter takes a light reading from a small spot in the center of the view finder while basically ignoring the proper readings for the rest of the frame. Exact spot metering will measure a centered area of about 1-2 percent, while partial metering will measure about 9-10 percent of the centered area.
This mode is best for when you want the subject properly exposed and you are not too concerned about getting the proper exposure for the rest of the image. Since this metering mode will not always produce desired results for a lot of casual users, it is not always available on point and shoot cameras.
Center Weighted Metering
This is the most common metering mode used in digital cameras. This mode assumes the main subject will be somewhere in the center of the frame and the camera will attempt to expose that area properly. The exposure for the rest of the frame will be averaged out. In other words, if the area outside the center of the frame contains light and dark areas, the center will be properly exposed, and the remaining areas will be averaged to come as close to the proper exposure as possible.
Be aware that this mode is heavily weighting the area in the center of the frame. So if your subject is off center or if the backgrounds are extreme light and dark contrasts, there might be an incorrect exposure. However, this mode works fine for the majority of picture taking situations.
Evaluative or Matrix Metering
This is the most advanced mode, and it comes with most cameras that offer metering options. In this case the meter will take light readings from different areas in the frame instead of just in the middle area. It also takes into account the position of the subject as well as the brightness or darkness of the foreground and background areas. Here comes the best part; The camera then compares your meter readings to a database of thousands of average photos.
It will then select an exposure that is typical for the type of scene you are shooting. That’s right, the meter is guessing! But don’t worry. The data base that it uses is so large that whatever you are shooting is probably typical of a ton of images stored in the database. This method is not 100 percent foolproof, but it’s more than OK for the average photographer.
Your camera will contain one or more of these modes. Shooting pictures on automatic will yield great shots without you having to worry about which setting to use. However, if you have the option of choosing your metering mode, try experimenting with different ones. You never know when a situation might arise where a change might be the best choice.
About the Author:
Keith Jones writes for http://easybasicphotography.com. A site geared towards beginners through serious amateurs who want to learn a little more about basic digital photography.
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