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Auto exposure lock (AEL)

Once you decide on a metering mode, you can use auto exposure lock (AEL) to tell the camera which part of the scene you want to base the exposure on. The settings will then be locked, so nothing changes while you recompose (move your subject somewhere besides the center of the frame) and take the picture. (See Chapter 10, "Zero to Hero: Better Photos Are Yours for the Taking," for details on photographic composition.)

To give you an idea of how powerful AEL can be, take a look at Figure 4.5 and Figure 4.6. Believe it or not, they were captured in the same scene, with the same lighting conditions, just moments apart. The only difference is that Figure 4.5 was captured with the exposure locked on the bright sunny scene outside the window, and the exposure in Figure 4.6 was locked on my friend Paul (inside).

Figure 4.5

Figure 4.5 Exposure is locked on the bright, sunny scene outside the window.

Figure 4.6

Figure 4.6 Exposure is locked on my friend Paul (inside).

Auto Exposure Lock

On most cameras, auto exposure lock is already programmed into the shutter button. (Check your user guide to know for sure; some cameras have a dedicated AEL button.)

Using auto exposure lock is simple. Just follow these steps:

  1. Position your subject in the center of your frame (Figure 4.7).
    Figure 4.7

    Figure 4.7 Positioning your subject in the center of the frame is the first step when using auto exposure lock.

  2. Press the shutter button halfway down to lock in the exposure.
  3. Continue to hold the button halfway down while you reposition the subject where you want it to be within the frame (Figure 4.8). You'll notice that as you move the camera around, pointing it at different objects, the exposure is locked and does not change.
    Figure 4.8

    Figure 4.8 After locking the exposure, recompose the scene to position the subject where you want it before taking the picture.

  4. Press the shutter button the rest of the way when you're ready to take the picture.

That's it. Simple, right?

Remember, just because you have to put your subject in the center of the frame to help the meter get the exposure right, doesn't mean you have to leave it there while you take the picture! See Chapter 10 for more about composition.

How Would You Use this in Real Life?

Take a look at Figure 4.9, captured without AEL, using evaluative (matrix) metering mode. Because this mode averages exposure data from across the whole scene, it got tripped up by the brighter background outside the window (behind the subject) and overcompensated with an exposure that's too dark.

Figure 4.9

Figure 4.9 Using the default setting of evaluative metering mode, the camera averaged the whole scene together. Because the large, bright background was factored into the equation, the resulting image was underexposed.

With quite a bit of difference in brightness levels between where we sat (inside) and the outdoor patio behind Emir (outside), I switched the camera to spot metering mode to avoid averaging the two areas together. Then, I used AEL to let the camera know I wanted the exposure based on Emir's face. The result can be seen in Figure 4.10.

Figure 4.10

Figure 4.10 After switching to spot metering mode, I positioned Emir's face in the center of the frame to get the proper exposure, then used AEL to prevent the settings from changing while I repositioned him slightly off center and took the picture.

Why not Just Use Fill-Flash?

Whenever you're faced with extreme exposure differences within the same scene, you have choices about how you handle it. In the previous example, I chose to avoid flash for three reasons:

  1. I prefer the look of natural light to that of direct flash.
  2. Because Emir is sitting in front of a window, the flash would have created a glare behind him, which I definitely wanted to avoid.
  3. If I had used fill-flash, I wouldn't have this great example of AEL and spot metering mode to share with you!

Of course, there are advantages and disadvantages to either choice you make. In this case, I was able to avoid glare on the window behind Emir, but at a cost. In order to expose him correctly (without flash), the brighter area behind him ended up overexposed.

Photography is all about making choices. The trick is to know what your options are—and then choose accordingly. C'est la vie.

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