Metering Mode pt. 2 - Center-Weighted and Spot Metering

OK, so yeah, I've been gone for a month.  Not out-of-town gone, more the wife-had-surgery-work-went-bananas-at-the-same-time type of gone.  But regardless, I'm back, and we need to continue our photo education, so lets get to it.

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In the last post we talked about matrix metering, which involves some pretty complex decision making on the part of the camera.  Now let's get into center-weighted and spot metering modes, which are much simpler and more predictable.

Center-weighted metering behaves the most like the classic "average luminance" metering we discussed in the first post on metering.  There is one difference however.  As implied by the name, center-weighted metering cares more about the center of the frame than the edges.  When I say the center, I mean a circle or oval taking up about 50-70% of the frame (the actual area being measured depends on your camera).  Center-weighted metering will suggest exposure settings that render this circle / oval area a medium gray, with some minor consideration given to very dark or very bright areas at the periphery of the frame.

There are two great thing about center-weighted metering:

1. It's predictable.
2. It prioritizes the center of the frame (where your subject tends to be located a lot of the time).

Center-weighted metering is good in situations where the center of the frame needs to be properly exposed and the edges don't matter.  For example, a portrait where the sun is setting right behind your subject, or a still-life shot of a leaf, sitting in a pool of light on the otherwise dark forest floor.  Makes sense right?

Now let's move on to spot metering.  Spot metering only measures a tiny portion of the frame (normally 2-5% of the total image area).  This spot is always in the center of the frame, although in some newer professional cameras it is possible to move the spot around.  Spot metering will suggest exposure settings that will make the object inside the spot appear a perfect 50% medium gray.

The two advantages of spot metering are:

1. It's almost perfectly predictable.
2. You can meter very small areas of the frame separately from each other.

Spot metering is good if you need a very precise meter reading for one tiny portion of the image and want to ignore everything else.  Now remember, when you spot meter an object it's going to give you exposure values that will make that object medium gray.  If you're spot metering a light-toned object you'll have to overexpose compared to the meter reading.  If you're spot metering a dark object, you'll need to underexpose it somewhat.  Spot metering also works great with auto-exposure lock, another feature we will come to shortly.