Understanding different metering modes of Digital Cameras

Metering

To understand Metering system we can say that to burn the image on camera sensor, camera determines how much light is required. The measurement of light is called metering. And that measured final value is called Exposure.

This is automatically done in all modern digital cameras. You just need to select right metering mode out of 3 available.
These modes are

1.Matrix
2.Center-weighted
3.Spot

By selecting metering mode we are instructing which part of the image we want to be exposed. And all these 3 modes are used in specific lighting situations. Name of these modes may vary according to camera brands, but on my Nikon (D80) metering mode names are as stated above.

Choosing correct mode is not a difficult task as normally 80 % situations demand Matrix metering, I personally too use Matrix metering most of the time.
Am trying to explain the situations in which these are used as follows.

1. Matrix Metering

This mode normally offers best exposure and this is used when we want every part of the image is important and each area center or corner should be exposed properly. In this mode the scene is divided into matrix zones and each zone exposure is measured independently.
In Nikon cameras Matrix metering evaluates whole scene but more attention is given to the point of focus selected. Suppose your selected focus point is Center, then camera will try to expose whole scene but center of scene or whatever focus point is, will be developed more accurately.

2. Center-weighted

This is the mode which was most used one in old times when metering was not that much improved. But still it is used. This method averages the exposure of the entire frame but gives extra weight to the center.

3. Spot Metering

Spot metering allows you to meter the scene at the selected focus point only. Some cameras dont allow to select the focus point and just meters at center of scene, but Nikon & Sony allows and Spot metering can be done for any selected focus point. Only a small area of the whole frame is metered and the exposure of the rest of the frame is ignored. Spot metering needs to be used very carefully. It is useful for brightly backlit, macro, moon shots & night shots.

But you should ask how camera determines exposure with all these different modes, Camera does that by adjusting Shutter speed.

At Spot metering shutter speed is increased and at Matrix metering shutter speed is deceresed to get more light and expose whole scene