Metering Modes in Photography
This is how subject brightness is measured by the camera. This is because the amount of light reflected by different subjects vary. Bright subjects will reflect more light compared to darker subject. The camera is standardised in way that the middle grey is set as the reference colour. Middle grey is the colour deemed to be halfway between white and black. If it measured it is about 18% of reflected light by the subject. This means that if you have a subject that reflects more than 18% of light the camera will assume it is over-exposed, and if it reflects less that 18% of light, the subject is assumed to be under-exposed. Camera metering will work pretty well if the lighting is evenly distributed in the scene but in instances where there is high contrast in lighting the camera might find it hard to get balanced metering.
Most cameras offer different metering modes in case you encounter varying lighting in a scene:
Evaluative/Matrix/Overall Metering:It takes into consideration
everything in your frame i.e. the camera measure the light intensity of several
points of the scene and gets the average exposure.This is usually the default metering setting since it is assumed that most of the time the lighting in your scene will
have even distribution of lighting
Spot/Partial Metering: this measures a small area in the scene, without being influenced by other areas in the scene. It can be at the centre on another part depending on whether your camera has got the function to change from the centre. This makes it very useful in high contrast scenes since the camera is able to identify the most important part of your scene. In cases where the background is too bright or too dark compared to the subject, spot metering will concentrate on the subject and exclude the background making your subject to be well exposed without being influenced by the lighting in the background.
Centre Weighted Metering: it emphasizes largely on the centre, it means the meter will give over 75% emphases on the material at the centre of the frame. This makes it less influenced by other parts at the edges of the scene that may be in contrast with the subject which is particularly useful when the subject takes quite a significant area on the scene i.e. it occupies a large space. This assumes that most of your subjects are mostly placed at the centre, so ensure that your subject is placed at the centre when using this mode.
Metering can be used in combination with Exposure compensation whereby you trick your camera into allowing more light to compensate for inadequate lighting. To lighten up your subject you increase the exposure compensation by 1 stop, you specify +1 to open the aperture or slow down the shutter speed. You use this when you have bright backgrounds than the subject. To darken the subject you decrease the exposure compensation by 1stop, you specify -1 to reduce the aperture or increase the shutter speed. How much exposure compensation you need to set depends on the tonality of the background and the effect you are trying to achieve.