Canon EOS 5D Mark III Instruction Manual (en)

Exposure compensation can brighten (increased exposure) or darken 
(decreased exposure) the standard exposure set by the camera.
Exposure compensation can be set in the d/s/f shooting modes. 
Although you can set the exposure compensation up to ±5 stops in 1/3-
stop increments, the exposure compensation indicator in the viewfinder 
and on the LCD panel can only display the setting up to ±3 stops. If you 
want to set the exposure compensation setting beyond ±3 stops, you 
should use the Quick Control (p.49) or follow the instructions for [z2: 
] on the next page.
Check the exposure level indicator.
Press the shutter button halfway (0) 
and check the exposure level indicator.
Set the exposure compensation 
While looking at the viewfinder or 
LCD panel, turn the <5> dial.
If it cannot be set, set the <R> 
switch to the left, then turn the <5> dial.
Take the picture.
To cancel the exposure 
compensation, set the exposure 
compensation amount back to <
Setting Exposure CompensationN
Increased exposure for a 
brighter image
Decreased exposure for a 
darker image
If [z2: Auto Lighting Optimizer] (p.144) is not set to [Disable], the image 
may still look bright even if a darker exposure compensation amount has been set.
The exposure compensation amount will remain in effect even after you 
set the power switch to <2>.
After setting the exposure compensation amount, you can set the 
<R> switch to the right to prevent the exposure compensation 
amount from changing accidentally.
If the exposure compensation amount exceeds ±3 stops, the end of the 
exposure level indicator will display <I> or <J>.