LIoP will re-open on the 22nd of June 2020
Camera makers started adding multiple metering sensors in an effort to produce better exposures.
One of the earliest types of multiple sensor metering systems was center-weighted metering and it is still used. This system takes readings from across the scene but favours the central area for the exposure reading.
All cameras now also include spot or partial metering. These are isolated meters and usually meter the very centre of the image. So this is measuring a very specific part of a scene… like a shadow or a highlight! You can select a different off-centre spot, or recompose an image by moving the camera after metering.
For example, you would use spot or partial metering on a bright sunny day when the light is creating shadows. You could decide to measure the light reflecting from the highlight and expose this correctly, the shadows will fall darker in the image. Or you could expose for the shadows and the highlights will overexpose. Another example is if you are on snow, sand or water your subject could underexpose unless you use flash or spot/partial meter on their face to expose for them correctly, overexposing the snow, sand or water which will look brighter and better!
Then there is also a system called Evaluative (or Matrix) which measures 100% of the scene. This allows for varied sensors placed across the image area. It can “throw out’ areas that are too bright or dark and find a much better exposure. Evaluative or Matrix can be used anytime but especially on overcast days where the light is even.