Canon EOS 1D Mark III User Guide - Page 19

Also, the secondary image-forming lens is optimized for the f/5.6 and f/2.8 light flux by having a different surface shape for the respective light flux entering the lens. The top and bottom light flux is compatible with f/5.6, while the left and right light flux is compatible with f/2.8. The rear side of the secondary image-forming lens features a newly-developed aspherical surface compatible with f/2.8 lenses. AF Start Button The EOS-1D Mark III has a new AF Start (AF-ON) button that can be used to execute AF and metering. We know that many pros using the EOS-1D series cameras have set C. Fn 04-1 to use the AE lock button for AF. The technique is called "autofocus with your thumb" or "back button focus." The 1D Mark III now provides a new AF start button dedicated to AF. Pressing the AF start button executes AF and metering. C. Fn IV-1,3 (AE lock/metering + AF start) is equivalent to C. Fn 04-1 in previous cameras. AF Point Selection The AF points can be put to work in several different ways. First, the AF points can be automatically selected by the camera from among the 45 points. Second, any one of 19 can be selected manually by the user. With C. Fn III -9-1/2, the manually-selectable AF points can be limited to 9 inner or outer AF points (including the center AF point). The AF point selection procedure is the same in either case. Press the AF selection button, then turn the Quick Control Dial or Main Dial to select the desired AF point. Pressing the Multi-Controller will select the center AF point. With the center AF point selected, pressing the Multi-Controller will set automatic AF point selection. C.Fn III -9-0: 19 points C.Fn III -9-1: 9 points (Inner) C.Fn III -9-2: 9 points (Outer) Automatic selection Automatic selection Automatic selection Automatic selection Automatic selection Automatic selection Quick Control Dial Main Dial Focusing Computation As with the EOS-1D Mark II N, two separate CPU processors are used, one for AF processing (including lens driving) and one for the camera. To attain 10 fps with AI Servo AF, the AF CPU and camera CPU are both the latest microcomputers (AF CPU: 48 MHz, 32-bit RISC; Camera CPU: 40 MHz, 32-bit RISC). The computing speed is 3 times faster than the 1D Mark II N's CPUs. V. INCOMPARABLE EOS AUTOFOCUS, NOW EVEN BETTER 19