Canon EOS 7D Instruction Manual page 91

If [8C.Fn III -12: Orientation linked AF point] is set to [1: Select
different AF points], you can set the AF area selection mode and
manually-selected AF point (or zone in the case of Zone AF) separately
for vertical and horizontal shooting (p.214).
If [8C.Fn III -10: Focus display in AI SERVO/MF] is set to [Disable],
the active AF points <S> during AI Servo AF will not be displayed.
AF-Assist Beam with the Built-in Flash
Under low-light conditions, when you press the shutter button halfway,
the built-in flash fires a brief burst of flashes. It illuminates the subject to
enable easier autofocusing.
The built-in flash's AF-assist beam is effective up to about 4 meters/13.1
feet.
In the d/s/f/a/F shooting modes, press the <I> button to pop-
up the built-in flash. Then it will fire the AF-assist beam when necessary.
Lens' Maximum Aperture and AF Sensitivity
With lenses whose maximum aperture is larger than f/5.6
With all AF points, cross-type AF sensitive to both vertical and
horizontal lines is possible.
With lenses whose maximum aperture is larger than f/2.8*
With the center AF point, high-precision, cross-type AF sensitive to both
vertical and horizontal lines is possible. The center AF point's sensitivity
to vertical and horizontal lines is about twice as sensitive as the other
AF points.
The remaining 18 AF points will work as cross-type points with lenses
brighter than f/5.6.
* Except with the EF 28-80mm f/2.8-4L USM and EF 50mm f/2.5 Compact Macro lenses.
AF Area Selection Modes
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