You might never notice it, but when you press the shutter button to take a picture with flash enabled, the Canon EOS 60D emits a brief preflash before the actual flash. This preflash is used to determine the proper flash power needed to expose the image.
Occasionally, the information that the camera collects from the preflash can be off-target because of the assumptions the system makes about what area of the frame is likely to contain your subject. To address this problem, your camera has a feature called Flash Exposure Lock, or FE Lock. This tool enables you to set the flash power based on only the center of the frame.
Unfortunately, FE Lock isn’t available in Live View mode. If you want to use this feature, you must abandon Live View and use the viewfinder to frame your images.
Follow these steps to use FE Lock:
With your pop-up flash up and ready, frame your photo so that your subject falls under the center autofocus point.
You want your subject smack in the middle of the frame. You can reframe the shot after locking the flash exposure, if you want.
Focus manually or by using autofocus, in which case you press the shutter button halfway or use AF-ON to initiate autofocus.
Although you can release the shutter button if you like, it’s better to hold it down so you don't have to reestablish focus later.
While the subject is still under the center autofocus point, press and release the AE Lock button.
The camera emits a preflash, and the letters FEL display for a second in the viewfinder. You also see the asterisk symbol (the one that appears above the AE Lock button on the camera body) next to the flash icon in the viewfinder.
If needed, reestablish focus on your subject.
Reframe the image to the composition you want.
While you do, keep the shutter button pressed halfway (or hold AF-ON) to maintain focus if you’re using autofocus.
Press the shutter button the rest of the way to take the picture.
The image is captured using the flash output setting you established in Step 3.
FEL is also helpful when you’re shooting portraits. The preflash sometimes causes people to blink, which means that with normal flash shooting, in which the actual flash and exposure occur immediately after the preflash, their eyes are closed at the exact moment of the exposure. With FEL, you can fire the preflash and then wait a second or two for the subject’s eyes to recover before you take the actual picture.
Better yet, the flash exposure setting remains in force for about 16 seconds, meaning that you can shoot a series of images using the same flash setting without firing another preflash at all.