Canon EOS 5D EOS 5D Instruction Manual - Page 75

f Selecting the AF ModeN One-Shot AF for Still Subjects AF point Focus confirmation light Pressing the shutter button halfway activates the autofocus and achieves focus once. X The AF point which achieves focus flashes briefly. At the same time, the focus confirmation light in the viewfinder is displayed. X With evaluative metering, the exposure setting (shutter speed and aperture) will be set when focus is achieved. The exposure setting and focus will be locked as long as the shutter button is pressed halfway. (p.79) You can then recompose the shot while retaining the exposure setting and point of focus. If focus cannot be achieved, the focus confirmation light in the viewfinder will blink. If this occurs, a picture cannot be taken even if the shutter button is pressed fully. Recompose the picture and try to focus again. Or see "When Autofocus Fails (Manual Focusing)" (p.80). AI Servo AF for Moving Subjects While you press the shutter button halfway, the camera focuses continuously. This AF mode is for moving subjects when the focusing distance keeps changing. X With predictive AF*, the camera can also focus track a subject which steadily approaches or retreats from the camera. X The exposure is set at the moment the picture is taken. 75