Canon EOS 5D Mark III Instruction Manual (en)

The camera’s AF sensor has 61 AF points. The illustration below shows 
the AF sensor pattern corresponding to each AF point. With f/2.8 or 
larger maximum aperture lenses, high-precision AF is possible at the 
viewfinder center.
Depending on the lens attached to the camera, the number of 
usable AF points and AF pattern will differ. For details, see pages 
79 to 85.
About the AF Sensor
These focusing sensors are geared to obtain higher precision 
focusing with f/2.8 or larger maximum aperture lenses. A diagonal 
cross pattern makes it easier to focus subjects that may be difficult 
to focus. They cover the five vertical AF points at the center.
These focusing sensors are geared to obtain high-precision 
focusing with f/4 or larger maximum aperture lenses. Since 
they have a horizontal pattern, they can detect vertical 
These focusing sensors are geared for f/5.6 or larger 
maximum aperture lenses. Since they have a horizontal 
pattern, it can detect vertical lines. They cover the three 
columns of AF points at the viewfinder’s center. The center 
AF point, and the AF points above and under the center AF 
point are geared for f/8 or larger maximum aperture.
These focusing sensors are geared for f/5.6 or larger 
maximum aperture lenses. They can detect horizontal lines 
and cover all 61 AF points in a vertical pattern. The center 
AF point, and the AF points on the left and right of the center 
AF point are geared for f/8 or larger maximum aperture.
Cross-type focusing: f/4 horizontal + f/5.6 vertical
f/5.6 vertical 
Dual cross-type focusing: 
f/2.8 right diagonal + f/2.8 left diagonal
f/5.6 vertical + f/5.6 horizontal
Cross-type focusing: 
f/5.6 vertical + f/5.6 horizontal