Overriding Autoexposure Results with Exposure Compensation

When you set your camera to the P, Tv, Av, or A-DEP exposure modes, you can enjoy the benefits of autoexposure support but still retain some control over the final, overall exposure. If you think that the image the camera produced is too dark or too light, you can use a feature known as exposure compensation, which is sometimes also called EV compensation. (The EV stands for exposure value.)

Whatever you call it, this feature enables you to tell the camera to produce a darker or lighter exposure than what its autoexposure mechanism thinks is appropriate. Best of all, this feature is probably one of the easiest on the whole camera to understand. Here's all there is to it:

✓ Exposure compensation settings are stated in terms of EV values, as in +2.0 EV. Possible values range from +2.0 EV to -2.0 EV.

✓ A setting of EV 0.0 results in no exposure adjustment.

✓ For a brighter image, you raise the EV value. The higher you go, the brighter the image becomes.

✓ For a darker image, you lower the EV value. The picture becomes progressively darker with each step down the EV scale.

Each full number on the EV scale represents an exposure shift of one full stop. In plain English, that means that if you change the exposure compensation setting from EV 0.0 to EV -1.0, the camera adjusts either the aperture or shutter speed to allow half as much light into the camera as you would get at the current setting. If you instead raise the value to EV +1.0, the settings are adjusted to double the light.

By default, the exposure is adjusted in 1/3 stop increments. In other words, you can shift from EV 0.0 to EV +0.3, +0.7, +1.0, and so on. But you can change the adjustment to 1/2-stop increments if you want to shift the exposure in larger jumps — from EV 0.0 to EV +0.5, +1.0, and so on. To do so, display Setup Menu 3, highlight Custom Functions, and press Set. Then select Custom Function 1, press Set, and press the up or down cross key to change the setting. Press Set again to lock in the new setting. If you make this change, the meter will appear slightly different in the Shooting Settings display and Live View display than you see it in this book. (There will be only one intermediate notch between each number on the meter instead of the usual two.) The viewfinder meter does not change, but the exposure indicator bar appears as a double line if you set the exposure compensation value to a half-step value (+0.5, +1.5, and so on).

Exposure compensation is especially helpful when your subject and background are significantly different in brightness. As an example, take a look at the first image in Figure 5-16. Because of the very bright sky in the background, the camera chose an exposure that left the palm tree too dark.

One way to cope with this situation is to adjust the exposure metering mode, as discussed earlier in this chapter. I took the images in Figure 5-16 in Evaluative mode, for example, which meters exposure on the entire frame. Switching to Partial metering might have done the trick, but frankly, I find it easier to use exposure compensation than to fool with metering mode adjustments in most situations. So I left the metering mode alone and just amped the exposure compensation setting to EV +1.0, which produced the brighter exposure on the right.

Brighter Exposure
Figure 5-16: For a brighter exposure than the autoexposure mechanism chooses, dial in a positive exposure compensation value.

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To apply exposure compensation, take these steps:

1. Hold down the Exposure Compensation button.

You can see the button in the margin here; it's the same one you use to adjust the f-stop when you shoot in manual exposure mode. (Refer to Figure 5-15.)

If the Shooting Settings display is active, the exposure meter becomes highlighted, as shown in Figure 5-17. Again, the purple highlight and the two pointers at the edges of the highlighted area are there to remind you that you can now adjust the setting with the Main dial. If you're looking through the viewfinder or shooting in Live View mode, the meter appears as usual.

Exposure Compensation setting

Exposure Compensation setting

Canon Exposure Dial
Figure 5-17: In autoexposure modes, the meter indicates the exposure compensation setting.


2. While keeping the button pressed, rotate the Main dial to change the exposure compensation value.

As you rotate the dial, the exposure indicator moves right or left along the exposure meter.

• Rotate the dial to the left to lower the value and produce a darker exposure. In Figure 5-17, for example, I dialed in a setting of EV -1.0.

• Rotate the dial to the right to raise the value and produce a brighter exposure.

• To return to no adjustment, rotate the dial until the exposure indicator is back at the center position on the meter.

3. Release the Exposure Compensation button after you select the value you want to use.

How the camera arrives at the brighter or darker image you request depends on the exposure mode:

✓ In Av (aperture-priority) mode, the camera adjusts the shutter speed but leaves your selected f-stop in force. Be sure to check the resulting shutter speed to make sure that it isn't so slow that camera shake or blur from moving objects is problematic.

✓ In Tv (shutter-priority) mode, the opposite occurs: The camera opens or stops down the aperture, leaving your selected shutter speed alone.

✓ In P (programmed autoexposure) and A-DEP mode, the camera decides whether to adjust aperture, shutter speed, or both to accommodate the exposure compensation setting.

These explanations assume that you have a specific ISO setting selected rather than Auto ISO; if you do use Auto ISO, the camera may adjust that value instead.

Keep in mind, too, that the camera can adjust the aperture only so much, according to the aperture range of your lens. The range of shutter speeds is limited by the camera itself. So if you reach the ends of those ranges, you either have to compromise on shutter speed or aperture or adjust ISO.

One final, and critical point about exposure compensation: When you power off the camera, it doesn't return you to a neutral setting (EV 0.0). The setting you last used remains in force for the P, Tv, Av, and A-DEP exposure modes until you change it.

Digital Cameras For Beginners

Digital Cameras For Beginners

Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.

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  • Jesse
    What is the exposure value range of a 1000d?
    8 years ago

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