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Function Junction, Part Deux: Metering, Auto Exposure Lock, Focus, and Drive

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You may not change your metering mode or focus drive the way you change your socks, but if you run into a jam (or your three-year-old gets ahold of your camera and manages to change all the settings), it's infinitely helpful to know what you're dealing with.
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Just when you thought we were running out of bells and whistles to talk about, I'm here to say, "But wait—there's more!" And it's true. Your camera is home to several additional functions that are pretty darn slick.

If your mind is still numb from the long list of goodness in the previous chapter, and even if you're thinking, "Advanced features? I'll never use those!"—don't abandon ship!

You may not change your metering mode or focus drive the way you change your socks, but if you run into a jam (or your three-year-old gets ahold of your camera and manages to change all the settings), it's infinitely helpful to, at least, know what you're dealing with, let alone how to fix it. So hang in there; you're making progress!

Metering modes

As you learned in Chapter 2, "Shooting Mode Bonanza: Getting Bossy, and Learning to Like It," metering is what your camera does to determine proper exposure. It's the process of measuring the light in a given scene and calculating an exposure based on those measurements, and—as luck would have it—there are several different ways to do it.

You may be wondering, "Why would anyone want or need more than one way to meter the light in a scene?" What a great question! To understand the answer, it helps to understand how the meter works.

Your camera's built-in light meter works by measuring the light reflecting back from whatever is in front of your lens. In any given scene, you may have some objects that reflect a lot of light and others that reflect substantially less. This presents a challenge when it comes to metering, because it's entirely possible to have areas of extreme brightness next to areas of considerable darkness, which will need to be reconciled in one form or another.

It's also not uncommon to find yourself in a situation where a large light source is actually behind your subject rather than in front of it, as when you are photographing people standing in front of a bright window.

This can make it tricky to get the exposure right, resulting in photos you may not be so fond of. Therefore, it's helpful to have a way to tell your camera which part of the scene you care about the most (which part you want to be sure is properly exposed). When combined with "auto exposure lock" (explained later in this chapter) you will be a force to be reckoned with!

As always, there's a chance your specific camera manufacturer may refer to these modes by different names or with sligshtly different icons, but the way they operate is pretty standardized. If you come across anything confusing, check your user guide for answers.

Before we get into how each mode works, grab your camera and take a moment to figure out how to access the metering modes of your particular model. The options available will vary from model to model, and finding them may be a bit trickier than finding your flash or white balance options from Chapter 3, "Function Junction: Flash, White Balance, and Exposure Compensation."

A few camera models have a dedicated button for metering modes, but on most others, you'll find them tucked into a menu option somewhere. You'll know you've found them when you either bump into a menu item conveniently called "metering modes," or you come across an icon that looks something like like.jpg. When in doubt, look it up!

In the following sections, we will take a look at these modes:

  • Evaluative or matrix metering
  • Center weighted
  • Partial
  • Spot

Evaluative (AKA Matrix)


Evaluative (matrix) metering mode is the PB&J of metering—and who doesn't like PB&J? The go-to metering mode for most situations, it works by metering the light across the entire scene, then averaging the whole thing together to create an exposure (Figure 4.1).

Figure 4.1

Figure 4.1 The shaded area represents the way evaluative (matrix) metering mode calculates exposure by averaging together light in the entire scene.

Because evaluative (matrix) mode is often considered to be general purpose, your camera is probably set here by default, which isn't necessarily a bad thing. It's a fine place to be—until you have problems, at which point you'll be glad there are other options.

Center Weighted


Although center-weighted metering mode still collects and averages exposure data from across the entire scene, the information gathered from the center area is given special consideration when it's figured into the final exposure calculation. In other words, the camera measures light across the whole scene, but it plays favorites with information gathered from the center, as depicted in Figure 4.2.

Figure 4.2

Figure 4.2 Even though center-weighted metering mode still calculates exposure by averaging the entire scene, it gives special consideration to the area in the center of the scene, as indicated by the overall shading with the darker shading in the center.



Unlike evaluative (matrix) and center-weighted modes, partial metering mode does not consider the entire scene when calculating exposure. Instead, it bases the exposure calculation on the area in the center of the viewable scene, as represented in Figure 4.3.

Figure 4.3

Figure 4.3 Unlike some of the other modes, partial metering mode does not consider the scene as a whole when determining exposure. Instead, it bases the entire calculation on a small area around the center of the frame, represented here with the shaded circle.

Because the meter is taking a targeted reading of a very specific part of the scene (rather than averaging the whole frame), you're able to tell the camera which part of the scene you want to base the exposure on by positioning it in the center of the frame, locking the exposure (with auto exposure lock, explained later in this chapter), then recomposing the scene as desired.

This is helpful in backlit situations where there is a lot of light coming from behind the subject (like when they're in front of a window or are being photographed outdoors on a ski slope where the surrounding snow could otherwise throw the exposure meter off balance). If you were to use a different mode, like evaluative, in such a situation, the camera would average the difference between the bright snow and the dark subject, resulting in an exposure that's not a good match for either.



Similar to partial metering, spot metering mode calculates exposure based only on a very specific point within the frame, rather than the scene as a whole. Compared to partial metering, spot metering targets an even smaller area within the center of the total frame, as shown in Figure 4.4.

Figure 4.4

Figure 4.4 The small shaded circle in the center of the frame represents the small and targeted area that area spot metering mode uses to calculate exposure. Similar to partial mode, spot metering mode does not consider the scene as a whole—only the very limited area in the center of the frame.

As with partial metering mode, this is useful if you're photographing a scene with backlighting or one where your subject occupies a small portion of the frame and the exposure varies dramatically from the rest of the scene, such as a person lit by a spotlight on an otherwise dark stage. When you use it with auto exposure lock (explained below), you can achieve especially pleasing results.

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