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The Rebel XSi's exposure compensation feature, along with the ability to review images in the LCD monitor, means you can quickly get good exposures without using mode. Exposure compensation cannot be used in mode; however, it makes the , , and modes much more versatile. Compensation is added (for brighter exposure) or subtracted (for darker exposure) in f/stop increments of 1/3 for up to +/– 2 stops (1/2 stop increments with C.Fn 1; see page 68).

To use the exposure compensation feature, start by pressing the shutter button halfway to turn on the metering system. Then press and hold (on back of the camera near the upper right corner of the LCD monitor). Rotate to change the compensation amount. The exact exposure compensation appears on the scale at the bottom of the viewfinder information display, as well as on the LCD monitor. (You can also adjust exposure compensation without turning on the metering system by just viewing the camera settings on the LCD monitor while pressing and turning .)

It is important to remember that once you set your exposure compensation control, it stays set even if you shut off the camera. Check your exposure setting as a regular habit (by looking at the bottom scale in the viewfinder information display) when you turn on your camera to be sure the compensation is not inadvertently set for a scene that doesn’t need it. Turn exposure compensation off (set it to zero) by holding and turning to set the scale on the LCD monitor or in the viewfinder back to zero.

With experience, you may find that you use exposure compensation routinely with certain subjects. Since the meter wants to increase exposure on dark subjects and decrease exposure on light subjects to make them closer to middle gray, exposure compensation may be necessary. For example, say you are photographing a high school soccer game with the sun behind the players. The camera wants to underexpose in reaction to the bright sunlight, but the shaded sides of the players’ bodies may be too dark. So you add exposure with the exposure compensation feature. Or maybe the game is in front of densely shaded bleachers. In this case the players would be overexposed because the camera wants to react to the darkness. Here, you subtract exposure. In both cases, the camera consistently maintains the exposure you have selected until you readjust the exposure settings.

The LCD monitor can come in handy when experimenting with exposure compensation. Take a test shot, and then check the photo and its histogram. If it looks good, go with it. If the scene is too bright, subtract exposure; if it’s too dark, add it. Again, remember that if you want to return to making exposures without using compensation, you must move the setting back to zero!

Autoexposure Bracketing (AEB): The Rebel XSi offers another way to apply exposure compensation: The Autoexposure Bracketing control (AEB). AEB tells the camera to make three consecutive exposures that are different: (1) A standard exposure (it uses any setting of the exposure compensation function as the standard); (2) An image with less exposure; and (3) One with more exposure. The difference between exposures can be set up to +/– 2 stops in 1/3 stop increments. (C.Fn 1 allows you to change this to 1/2 stop increments.) While using AEB, the Rebel XSi changes the shutter speed in mode and aperture in mode.

AEB is set through . Scroll to <AEB>, press , then use ◂▸ to set the amount. Three dots indicating the range of exposures appear on a small exposure scale on this menu. Make sure you press to accept the change.

When in Drive mode, you have to press the shutter button for each of the three shots. As you shoot, a marker appears on the exposure scale at the bottom of the viewfinder information display. This marker indicates which exposure is being used with the AEB sequence. In Drive mode, the camera takes the three shots and stops. When you use and , all three shots are taken. With , each of the shots at the end of the countdown is bracketed. This means if you set for six, you end up with 18 images; however, the camera buffer fills up quickly, so after the first couple shots are taken, the XSi waits until the images in the buffer are written to the memory card before the remaining shots are taken.

AEB can help ensure that you get the best possible image files for later adjustment using image-processing software. A dark original file always has the potential for increased noise as it is adjusted, and a light image may lose important detail in the highlights. AEB can help you to determine the best exposure for the situation. You won’t use it all the time, but it can be very useful when the light in the scene varies in contrast or is complex in its dark and light values.

AEB is also important for a special digital editing technique that allows you to put multiple exposures together into one master to gain more tonal range from a scene. You can take the well-exposed highlights of one exposure and combine them with the better-detailed shadows of another. (This works best with 1/2 stop bracketing.) If you carefully shot the exposures with your camera on a tripod, they will line up exactly so that when you put the images on top of one another as layers using image-processing software, the different exposures are easy to combine. (You may even want to set the camera to —in this mode it takes the three photos for the AEB sequence and then stops.)