What exactly is Metering?

this might be a stupid question but i just started photography and I tried switching the metering modes on my 50D and shooting the same photo with different metering mode. I don't see any difference on the photo...am I missing something? thanks all

Metering is the method of determining the amount of light that is falling on the subject. The most direct method of metering is to walk over to the subject and hold an incident light meter up next to them and take a direct measurement.

Your camera also has a meter, but it is not an incident light meter. Instead your camera has a reflective light meter. It measures how bright the subject appears to be and then makes an educated guess from that as to how much light is falling on it. The problem is that your camera meter has to assume the subject will be some middle tone, so really bright or dark scenes will confuse it and cause error.

Canon cameras have a few ways of using the meter to allow you to try and reduce error.

Evaluative - basically auto metering. The camera looks at the whole scene and makes a decision.
Average - the camera averages the brightness of the whole scene and tries to expose it to a middle tone.
Spot - let's you meter off a small part of the scene. If you know how bright that tone is you can very accurately meter with the camera.

Also-
Change the focal point to just that one center spot.
Experiment with placing it on different areas of a varied scene when you shoot.
Sometimes, too, you can zoom in to a certain place for exposue setting and, while holding that, zoom back out to the desired shot.

I keep mine on the center spot, mainly for focusing with Av mode.

This is a good manual by Revell that can help a lot with the 50D settings:

"Canon 50D: From Snapshots to Great Shots"
http://www.amazon.com …oks&qid=1256924​919&sr=8-1

Good luck.

There doesn't even need to be all that much difference.
Post #47
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Switching metering modes simply changes what AREA of the viewfinder is used to compute exposure, and how the surrounding areas might or might not bias the exposure reading. If you aimed at an 18% gray wall, all would be identical in the reading!

By reading one section of the viewfinder, by selecting which of the modes, the camera has a better chance of an accurate exposure reading when the surrounding area is especially bright/dark. All modes will be fooled when the main subject is brighter or darker than 18% gray, which is why the EC control exists to compensate for brighter/darker main subjects.