Canon EOS-1DS Mark III Instruction Manual page 85

Selecting the AF Point
Lens, Maximum Aperture and AF Sensitivity
The EOS=IDs Mark Jil can execute high-precision AF with lenses
whose maximum aperture is f12.8 or larger.
With f/2.8 and faster Jenses*
With the 19 AF points indicated by _,
high-precision, cross-type AF (both
horizontal- and verticaNine sensitive) is
possible. With cross-type AF, verticaNine
detection is about 2 times as sensitive as
horizontaNine detection. The remaining
26 Assist AF points are hodzontaNine
sensitive only.
* Excludingthe EF24mmf/2.8and EF28mmf/2.8.
With Jenses whose maximum aperture is f/4 or Jarger
If the maximum aperture of the lens or Extender and lens combination
is faster than f14, the center AF point will work as a high-precision,
cross-type point sensitive to both horizontal and vertical lines. The
remaining 18 AF points and the 26 Assist AF points work as horizontal-
line sensitive AF points.
With Jenses whose maximum aperture is f/5o6 or Jarger
With lenses whose maximum aperture is larger than ft5.6, aii the AF
points, including the Assist AF points, wiii be horizontal-line sensitive only.
With Jenses whose maximum aperture is f/8 or Jarger
With lenses whose maximum aperture is larger than f18, AF will be
possible with the center AF point which will be horizontal-line sensitive.
AF will not work with the other AF points.
@ when the EF70_200mm f!2.gL USMis used with an Extender, use the center
AF point only. The other AF points may cause a focusing error.
when Usingthe EF2@mm
f128 or EF28mm
f/2,8 fen s,
the 13 AF pointsshow_
_rOss:type Points ]he remaining 6 AF p0ints wil! be
harizontaNine sensitive.
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