Canon EOS-1D X Mark III EOS-1DX Mark III Advanced User Guide - Page 916

Group H The 23 AF points shown here are available for autofocusing. As the AF area selection mode, choose from Spot AF, 1-point AF, Expand AF area: , Zone AF (manual selection), or 23point Automatic selection AF. With an extender attached to extendable lenses, AF is available when maximum aperture is f/8 (in a range of f/5.6-f/8). : Cross-type AF point. Offers excellent subject tracking and high-precision focusing. : AF points sensitive to horizontal lines (AF points left and right of the center) or vertical lines (AF points above and below the center). : Disabled AF points (not displayed). Caution Expand AF area: applies to the 23 available AF points. Expansion for manually selected AF points that are not surrounded by active AF points is limited to any available adjacent points. If the maximum aperture value is slower than f/5.6 (greater than f/5.6 but not exceeding f/8), focus may not be achieved with AF when shooting low-contrast or low-light subjects. If the maximum aperture value is slower than f/8 (greater than f/8), AF is not possible during viewfinder shooting. 916