Canon EOS-5D Instruction Manual page 78

SSelecting the AF PointN
Selecting with the Dial
When looking at the LCD panel to select the AF point, note the following:
Automatic selection
top
If focus cannot be achieved with an EOS-dedicated, external Speedlite's
AF-assist beam, select the center AF point.
Lens' Maximum Aperture and AF Sensitivity
The EOS 5D will execute high-precision AF with lenses whose
maximum aperture is f/2.8 or larger.
With lenses whose maximum aperture is f/2.8 or larger*
With the center AF point, high-precision, cross-type AF sensitive to both
vertical and horizontal lines is possible. With cross-type AF, vertical-line
detection is twice as sensitive as horizontal-line detection. The other
eight AF points are horizontal-line sensitive or vertical-line sensitive.
*
Except with the EF28-80mm f/2.8-4L USM and EF50mm f/2.5 Compact Macro lenses.
With lenses whose maximum aperture is larger than f/5.6
The center AF point is a cross-type AF sensor. The other eight AF
points are horizontal-line sensitive or vertical-line sensitive.
78
Press the <S> button, then turn the
<6> dial or <5> dial to select the
AF point in the looping sequence
shown on the left.
, center
The spot metering circle has six invisible Assist AF
points (see left illustration) that function in the AI
SERVO AF mode. The
the same vertical-line sensitivity as the center AF
point at f/2.8, and the
horizontal-line sensitivity at f/5.6.
, right
Assist AF points have
Assist AF points have
,