Canon EOS 5D Mark III Instruction Manual (en)

Live View Shooting Cautions
Live View Image
Under low- or bright-light conditions, the Live View image may not reflect 
the brightness of the captured image.
If the light source within the image changes, the screen may flicker. If this 
happens, stop the Live View shooting and resume shooting under the 
actual light source to be used.
If you point the camera in a different direction, it may throw off the Live 
View image’s correct brightness momentarily. Wait until the brightness 
level stabilizes before shooting.
If there is a very bright light source in the picture, the bright area may 
appear black on the LCD monitor. However, the actual captured image 
will correctly show the bright area.
In low light, if you set the [52: LCD brightness] to a bright setting, noise 
or irregular colors may appear in the Live View image. However, the 
noise or irregular colors will not be recorded in the captured image.
When you magnify the image, the image sharpness may look more 
pronounced than it really is.
Custom Functions
During Live View shooting, certain Custom Function settings will not take 
effect (p.320).
Lens and Flash
The focus preset function is possible during Live View shooting only 
when using a (super) telephoto lens equipped with the focus preset 
mode marketed since the second half of 2011.
FE lock and modeling flash will not work if an external Speedlite is used.