Canon EOS 1D Instructions Manual page 72

AF Sensitivity and the Lens' Maximum Aperture
The EF 70-200mm f/2.8L USM lens (without IS) used together with Extender EF
1.4x or EF 1.4x II will enable the center AF point to work as a cross-type sensor.
However, do not autofocus with the other AF points because they may cause a
focusing error.
72
(3) With the following Extenders and L-series lenses whose
maximum aperture is faster than f/8, the center AF point will
be horizontal-line sensitive only. The other AF points cannot
be used for AF.
•
With Extender EF 1.4x or EF 1.4x II:
EF 400mm f/5.6L USM
EF 500mm f/4.5L USM
EF 100-400mm f/4.5-5.6L IS USM
•
With Extender EF 2x or EF 2x II:
EF 300mm f/4 L USM
EF 300mm f/4L IS USM
EF 400mm f/4 DO IS USM
EF 500mm f/4L IS USM
EF 600mm f/4L USM
EF 600mm f/4L IS USM
EF 70-200mm f/4L IS USM
•
When the < > button is pressed, the display
shown on the right will appear on the top LCD
panel.