Canon EOS 5D Mark III Instruction Manual (en)

You can magnify a captured image by approx. 1.5x to 10x on the LCD 
Magnify the image.
The image can be magnified during 
image playback (single-image display), 
during image review after image 
capture, and from shooting-ready state.
Press the <
u> button.
The magnified view will appear. The 
magnified area and [6
u] will be 
displayed on the lower right of the screen.
The image magnification increases 
as you turn the <6> dial clockwise. 
You can magnify the image up to 10x.
The image magnification decreases as 
you turn the <6> dial counterclockwise. 
Turning the dial further will display the 
index display (p.255).
Scroll around the image.
Use <
9> to scroll around the 
magnified image.
To exit the magnified view, press the 
u> button or <x> button and the 
single image display will return.
u Magnified View
Magnified area position
In magnified view, you can turn the <5> dial to view another image at the same magnification.
The image can be magnified also during the image review immediately after shooting.
A movie cannot be magnified.