Canon EOS-1D Mark IV - Manual (Page 99)

EB Selecting the AF Point
Maximum f/stop:
[Manual selection] Up to f/2.8
With the 39 AF points indicated by I, high-precision,
cross-type AF (both horizontal- and verticai-line
sensitive) Is possible during manual AF point
selection. The cross-type sensors' vertical-line
sensitivity is approx, two times higher than their
horizontal-line sensitivity. The remaining six AF
points will be horizontal-line sensitive.
During automatic AF point selection, the number of
cross-type AF points will decrease from 39 points to the
19 points indicated with I. The remaining 26 AF points
will be horizontal-line sensitive.
Maximum f/stop: f/4
High-precision, cross-type AF with the center AF point is possible. The
remaining 44 AF points will be horizontal-line sensitive only.
Maximum f/stop: f/5.6 or f/8
With f/5.6 lenses, all the AF points will be horizontal-line sensitive only.
With f/8 lenses, AF will be possible with the center AF point being
horizontal-line sensitive only. AF will not work with the other AF points.
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[Automatic selection]
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• In the case of zoom lenses whose maximum aperture varies depending
on the lens focal length, the AF points will be horizontal-line sensitive only
(They will not work as cross-type points). However, with the EF 28-80mm
f/2.8-4L USM lens, cross-type AF will work with the center AF point,
e With the EF 24mm f/2.8 or EF 28mm f/2.8 lens, the three AF points on
the extreme left and right of the /Vrea AF frame will be horizontal-line
sensitive (They will not work as cross-type points).
Q The following lenses and lens combinations have a maximum aperture of
f/4, but cross-type focusing on 39 AF points is still possible as with lenses
having an f/2.8 maximum aperture.
EF 17-tOmm f/4L USM, EF 24-105mm f/4L IS USM,
EF 70-200mm f/2.8L IS USM + Extender EF 1.4X II,
EF 200mm f/2L IS USM + Extender EF 2X II,
EF 300mm f/2.8L IS USM + Extender EF 1.4X II,
EF 400mm f/2.8L IS USM + Extender EF 1.4X II
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