Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 100)

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The camera’s AF sensor has 61 AF points. The illustration below shows
the AF sensor pattern corresponding to each AF point. When using
lenses with a maximum aperture of f/2.8 or faster, high-precision AF is
possible at the viewfinder center.
AF Sensor
Depending on the lens attached to the camera, the number of usable
AF points, AF point patterns, the shape of Area AF frame, etc. vary. For
details, see “Lenses and Usable AF Points” on page 102.
Diagram
Cross-type focusing:
f/4 horizontal + f/5.6 or f/8 vertical
f/5.6 or f/8 vertical focusing Dual cross-type focusing:
f/2.8 right diagonal + f/2.8 left diagonal
f/5.6 or f/8 vertical + f/5.6 or f/8 horizontal
Cross-type focusing:
f/5.6 or f/8 vertical + f/5.6 or f/8 horizontal