Metering is very important in digital SLR photography. If you're taking photos using Aperture Priority or Shutter Speed Priority, the exposure metering is what determines the other settings for a proper exposure. DSLR cameras usually have three options for exposure metering. The three options on digital SLR cameras are Matrix, Center-weighted, and Spot.

In the examples below, the photographs were taken in aperture priority mode so the metering determined the shutter speed. The white wall of the lighthouse was selected as the metering point for consistency in comparing.

In matrix metering, the camera's processor looks at the scene and magically decides what's important. The camera's processor takes an average from all the key elements of the photograph so that most things aren't too dark or too bright as you see in the example below.

Aperture Priority Mode

Aperture: f/3.2

Shutter Speed: 1/2500s 

ISO : 200

Center-weighted metering makes the selected point of the image the most important thing to meter, but still gives some consideration to the surroundings.  In the photograph below the shutter speed was lengthened so that the white lighthouse shows up brighter. The walls are still a little darker than I'd like them due to the bright sky being considered by the meter.

Aperture Priority Mode

Aperture: f/3.2

Shutter Speed: 1/2000s 

ISO : 200

Spot metering only meters the selected focal point of the image. In this setting your DSLR camera will meter one spot and doesn't care about anything else that might be in the photograph. In the image below the spot metering told the camera meter to only consider the brightness of the walls so it made the photo exposure a little longer to brighten them just a little bit more than the last photo. The tradeoff here is that elements of the photograph have a chance of being blown out as you see the sky is somewhat in this photo. 

Aperture Priority Mode

Aperture: f/3.2

Shutter Speed: 1/1600s 

ISO : 200

In high contrast situations it's very easy for a digital SLR camera to get confused. In these situations you'll want to use spot metering to tell the digital camera what the correct exposure is. You can either meter something important like a persons face or meter something less confusing outside of the viewfinder to get a more realistic exposure. The trick to doing this is metering a solid mid-tone such as grass or a red brick wall, then using the exposure lock to keep the setting, and then pointing the camera back to the main subject to take the digital photograph. 

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