Metering is how your camera decides what the correct shutter speed and aperture should be depending on the amount of light that goes into the camera and the sensitivity of the sensor. Nowadays DSLR cameras have a light meter built in which makes it so much easier than using a film camera. In the film days you would use a hand held meter, which are still used today actually but more on that another time.
Lets go over the three main different types of metering modes. There is also center-weighted average metering, but lets leave that one for now. It just means the metering is weighted at the center and then averaged for the whole scene.
If you point your camera at a very bright area, the middle bar will go to the + side showing there is too much light for the current exposure. If you point your camera at a very dark area, the bar will go to the - side, showing that there is not enough light. You would then need to increase or decrease your shutter speed to get to the middle which is the correct exposure, according to your built in camera meter.
BUT THIS IS WRONG
Built in camera meters work great when the scene is evenly lit. But, it gets challenging for built in light meters to determine the exposure when there are different light levels and intensities.
Example, if you are taking a picture of the blue sky with no clouds or sun in the frame, the image will be correctly exposed, because there is just one light level to deal with. This is why we as photographers love cloudy days!
Correctly metering gets a lot harder if you add some clouds and mountains etc. The meter now needs to think about the brightness of the clouds, brightness of the sky and try come up with the "correct" exposure. What usually happens is the meter will brighten up the sky a little bit to expose the white clouds otherwise the clouds would be over exposed.
So you have a bright background and a darker object or person and that really confuses the cameras meter. By focusing on the person the meter will try and expose for the darkness and brightness resulting in the background being blown out (over exposed)
So, why is the middle wrong?
The middle is wrong because the camera reads middle grey. If you take a picture of snow with the bar being in the middle, the snow will be grey. If you take a picture of something black with the bar in the middle it will also be grey.
Basically you want to expose to the right for brighter subjects and expose to the left for darker subjects. A black bear for example.... I would under expose by 1/3 or 2/3rds and bang, a perfect exposure. For snow I always over expose by 1 stop or even 2 stops!!
Try it and you will see what I mean.
This metering mode is suited for all purpose, portraits and even back lit subjects. The camera sets the exposure automatically to suit the scene BUT if you leave the bar in the middle it will still seem under exposed.
Really good for when the background is a lot brighter than the subject. Partial metering covers around 9.4% at the centre of the view finder.
Feel free to mail me using the contact form if you have any questions about metering.
I love spot metering! This meters for a specific area of the scene. It only covers 2.3% of the area and works brilliatntly for control of exposure of the skin ignoring the background. I use it for 80% of my work.