Flash Exposure Compensation (FEC) is much like Auto Exposure Compensation in that you can increase or decrease flash exposure up to +/-2 stops in 1/3-stop increments. A positive compensation increases the flash output and a negative compensation decreases the flash output. The compensation is applied to all flash exposures until you reset the compensation back to 0. As with non-flash exposure, the camera is calibrated for an "average" scene of 18 percent gray, and flash exposures can be thrown off by very light and very dark subjects or scenes. As a result, very light subjects may need increased flash exposure ranging from +0.5 to +1.5 stops. Dark-toned subjects may need a flash reduction of approximately -1 to -2 stops. Some experimentation is required because subject and scene tonality varies.
If you use flash compensation to create a more natural-looking portrait in daylight, try setting negative compensation it between -1 and -2 stops. Also be aware that in bright light, the camera assumes that you're using fill flash to reduce dark shadows and automatically provides flash reduction. Experiment with the Rebel XSi/450D in a variety of lighting to know what to expect.
It's important to note that if you use FEC, you may not see much if any difference with negative compensation because the XSi/ 450D has Auto Lighting Optimizer turned on by default for all JPEG images. This feature automatically corrects images that are underexposed or have low contrast. So if you set FEC to a negative setting to reduce flash output, the camera may detect the image as being underexposed (too dark) and automatically brighten the picture.
7.2 This image was taken with the built-in flash with no flash output modifications. The main light is from a window to camera left. A large silver reflector is positioned to camera right. The dark shadow behind the dog is a disadvantage of using unmodified flash. Exposure: ISO 100, f/4, 1/15 second, Av mode, custom white balance.
If you're using FEC, it's best to turn off Auto Lighting Optimizer. Just go to the Set-up 3 (yellow) menu, and then press the down cross key to select Custom Functions (C.Fn). Press the Set button. Press the right or left cross key until the C.Fn II: Image, Auto Lighting Optimizer screen appears and the number 6 is displayed in the box at the top right of the screen. Press the Set button to activate the option controls. Press the down cross key to select option 1: Disable, and then press the Set button. The Auto Lighting Optimizer remains disabled in Creative Zone Modes until you enable it again.
7.3 For this image, flash exposure compensation was set to -1 Exposure Value (EV). The lowered flash exposure provides a more natural appearance than straight-on flash and lightens the shadow behind the dog. Exposure: ISO 100, f/4, 1/15 second, Av mode.
If you use an accessory Speedlite, you can set FEC either on the camera or on the Speedlite. However, the compensation that you set on the Speedlite overrides any compensation that you set on the XSi/450D's Set-up 2 (yellow) camera menu. If you set compensation on both the Speedlite and the camera, the Speedlite setting overrides what you set on the camera. So set compensation either on the Speedlite or on the camera, but not on both.
FEC can be combined with Exposure Compensation. If you're shooting a scene where one part of the scene is brightly lit and another part of the scene is much darker —for example, an interior room with a view to the outdoors —then you can set Exposure Compensation to -1 and set the FEC to -1 to make the transition between the two differently lit areas more natural.
To set FEC for the built-in flash, follow these steps:
1. Set the camera to a Creative Zone mode such as P, Tv, Av, M, or A-DEP.
2. Press the Menu button, and turn the Main dial to select the Shooting 2 (red) menu.
3. Press the down cross key to select Flash exp comp, and then press the Set button. The
4. Press the left cross key to set negative compensation (lower flash output) or press the right cross key to set positive flash output (increased flash output). As you make changes, a tick mark under the Exposure Level meter moves to indicate the amount of FEC in 1/3-stop increments. The FEC is displayed in the viewfinder when you press the Shutter button halfway. The FEC you set on the camera remains in effect until you change it.
To remove FEC, repeat these steps, but in Step 2, press the left or right cross key to move the tick mark on the Exposure Level meter back to the center point.
7.4 For this image, I used the Canon 580 EX Speedlite and bounced it off a white card held above the flash head. The exposure on the schnauzer is good, but the background shadow is still objectionable. Using another Speedlite to light the background would eliminate the shadow. Exposure: ISO 100, f/4, 1/6 second, Av mode.
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