Can someone please explain metering to me?

[Xyttik]

In some of the photography books I've read, they talk about how metering gives the best exposure, but never properly explain how to do it.

Is metering the technique that should be used when trying to take pictures of images with bright backgrounds?
Are there other helpful uses for it?

Can someone please de-mystify it for me? =)

 

[Robin Usagani]

Understanding Camera Metering and Exposure

 

[Big Mike]

It's can be a fairly involved topic....but I'll see if I can sum it up here.

The first thing you need to know, is that your camera (like all 'auto' capable cameras) has a built-in light meter. It's a 'reflected' light meter, it reads light that is reflecting off of things. The meter is calibrated to give you proper exposure for a subject that is 'middle grey'. It has to be calibrated to something....and middle grey is it.

So when you activate your camera's meter (half press the shutter release), it reads the scene in front of the lens. It assumes that what it's seeing, is middle grey (or that it will average out to middle grey) and it gives you the settings (aperture, shutter speed & ISO) that will get you your exposure. That's how metering works...but that's not the whole story.

So, because the meter in the camera reads reflected light...it can be fooled. Objects that we see as bright, reflect more light....objects that we see as dark, reflect less light. So remember that the camera's meter will always assume that it's seeing a scene that is middle grey. So when it sees something that is bright (like a white wall), it doesn't know that it's seeing a white wall...it just thinks that it's middle grey, but in bright light...so it gives you settings to lower the brightness, causing your photo to be underexposed. The opposite would happen with a black wall. The camera assumes that it's middle grey, but in low light, so it tries to give you more exposure...causing the photo to be overexposed.

So when we, as photographers, are 'metering'....we are trying to overcome this problem.
One way, would be to make the camera's assumption true. If it's expecting to see middle grey, then put a grey card in front of it. If the card is in the same light as your subject/scene, then the settings that the camera gives you, will be accurate. You just need to lock those setting in (manual mode is best). Then take the card away and compose your shot.

Another way would be to estimate the brightness of something in your scene, then adjust your exposure to the value that will give you proper exposure. For example, something white (snow, white wall) is probably about two stops brighter than middle grey. So if you can meter off of something white, you would adjust your exposure settings, not to zero on your scale (...-1...0...+1...), but to +2. That will get you proper exposure (or close to it).
The more practice & experience you get, the easier it is to estimate the brightness of different things, and then use that to set your exposure.

Another way to get proper exposure, probably the best way, would be to use a hand-held 'incident' light meter. Unlike the meter in your camera, this meter reads the light falling on the subject/scene, not the light reflecting off of it. And because it isn't influenced by how bright/dark the scene is, it gives you accurate exposure settings.

So....if you have a scene where your subject is quite a bit different than your background, you have to be aware of what the camera is metering/seeing. Different metering modes will tell the camera where you want it to look. For example, spot metering uses just a small spot, ignoring the rest of the scene. Matrix/Evaluative takes the whole scene into account. You also have to make a choice, as the photographer, what parts of the scene you want to expose for. In many cases, you can't expose for everything, so you have to choose. For example, if you have a person with a bright background, you probably want to expose for the person, not the background.

There is a lot more to it, but hopefully that gets you started.

Oh, say Hi to Sir Peter for me.

 

[Xyttik]

Thank you so much =)

Now I have a bit more idea of what I'm actually messing around with

Also, not sure if you were trolling me, but Sir Peter has been dead for 10 years =)

Edit: Just realised you meant Peter Jackson >.<