Ever wondered how your camera makes sure you get the right exposure when you are not using manual settings? The camera has a way of metering the scene for the optimum exposure. Let me correct myself. The camera has several ways of metering the scene for the optimum exposure. On a DSLR you can choose one of the metering modes you’d like to use. Let’s see what these modes are and when they are best put to use.
In spot-metering the camera sets the exposure settings after evaluating a particular (user-defines) spot in the entire scene. This is a preliminary way of setting exposure automatically and mostly the off-spot areas in the image may remain underexposed or get overexposed. This works best when there is a high dynamic range in the scene and you have to force the camera to get the correct exposure for a particular area in the image. If you are shooting against light and do not have a flash, you can use spot metering to set the correct exposure for the subject irrespective of other areas in the scene.
While spot metering evaluates exposure for a spot, the center-weighted metering meters a (custom) larger spot in the image. In this case if you have a subject that covers a large area in the picture you may want to use center-weighted metering. This was one good metering mode until the matrix metering came.
The matrix metering measures exposure at multiple spots in the scene. It then compares the results with a number of manufacture provided situations. And then it uses the exposure corresponding to the best match. Nikon for example embeds around 30000 exposure scenes into their camera for matrix metering. When you use matrix metering, the camera will meter the exposure at various spots in the image, find the best match from the library and use that exposure. This works very well since matrix metering has become very sophisticated over the years. However it’s not unusual for the camera to get tricked into bad exposure settings in unusual scenes. It is at that time that you really need to know which metering mode to choose. For almost any use you can use matrix metering. However you may want to use center-weighted or spot metering in case you are covering a scene that has a high dynamic range.
Which one have you been using all this while?