AF Sensitivity and the Lens’ Maximum ApertureThe EOS-1Ds’s AF points are all horizontal-line sensitive. However, bright lenses with a large maximum aperture enable certain AF points to work as cross-type sensors for higher AF precision.
(1) With lenses whose maximum aperture is f/2.8 or faster (lower f/number), the AF points highlighted in the illustration will be cross-type sensors sensitive to both vertical and horizontal lines. The remaining 38 AF points will only be horizontal-line sensitive. The cross-type sensor’s vertical- line sensitivity is three times higher than the horizontal-line sensitivity.
(2) With the following L-series lenses whose maximum aperture is brighter than f/4 by lens only or with Extenders, the center AF point will be a cross-type sensor for high- precision AF. The remaining 44 focusing points will only be horizontal-line sensitive (except with EF 70-200mm f/2.8L USM + Extender EF 1.4x).
EF 28-80mm f/2.8-4L USM EF 300mm f/4L 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 USM
•With Extender EF 1.4x or EF 1.4x II: EF 200mm f/2.8L USM
EF 200mm f/2.8L II USM EF 300mm f/2.8L USM EF 300mm f/2.8L IS USM EF 400mm f/2.8L USM EF 400mm f/2.8L II USM EF 400mm f/2.8L IS USM EF 70-200mm f/2.8L IS USM
•With Extender EF 2x or EF 2x II: EF 135mm f/2L USM
EF 200mm f/1.8L USM
