Multi-point Autofocus System
Currently, top-line EOS cameras have 61 autofocus (AF) points, the most in their class. Two Canon cameras have this system—the EOS 5D Mark III, on sale since March 2012, and the EOS-1D X, announced in October 2011 and originally scheduled for sale in April 2012, but delayed until June 2012. The release of the 5D MkIII gave Canon the lead once again in this category; previously, its top-line cameras had 45 AF points, which led the industry until Nikon released its D3 and D300 DSLRs with 51-point AF systems.
A higher number of AF points increases the chances of a sharply-focused photograph in situations where the subject travels across the frame at high speeds (e.g., sports, birds). The number, type, features and performance of autofocus point array systems is likely to continue to evolve.
Having so many AF points also helps relieve the photographer from having to use the 'lock focus and recompose' method of framing a photograph, since the subject will most probably have been picked up by one or more of the AF points. Even though the camera is intelligent enough to select the correct AF point(s) most of the time, EOS cameras equipped with a multi-point AF system will still allow the photographer to manually select an AF point.
The EOS-3, EOS-1v, and all EOS-1D models prior to the EOS-1D X feature a 45-point AF system. Almost all Canon DSLRs introduced since late 2005, starting from the EOS 20D and the Rebel XTi (400D), feature a nine-point AF system in a diamond-shape formation. The EOS 5D, released in 2005, takes this 9-point AF system a step further by introducing six more 'invisible' AF points (i.e. not user-selectable) in helping the camera acquire focus faster during subject tracking. There are five exceptions to Canon's recent rule of a 9-point AF system. The EOS 1000D (Rebel XS) has the 7-point AF system of most older Canon DSLRs. The EOS 7D, released in 2009, has a 19-point AF layout, fitting essentially within the same diamond-shaped area of the frame as the nine-point layout. The EOS 5D Mark III, released in March 2012, and the EOS-1D X, released in June 2012, have 61-point AF layouts. The EOS 6D, announced in September 2012, has an 11-point layout.
For the earlier generation of 45-point AF system, the central column of 1 or 2 sensors (7 in all up to EOS-1Ds Mk II, EOS-1D Mk II N) are cross-type sensors, which are sensitive to both vertical and horizontal lines to offer a high degree of accuracy. The EOS-1Ds Mk III, replaced by the EOS-1D X, has 19 cross-type sensors for higher accuracy, as well as placing the cross-type sensors to complement the Rule of Thirds. The other Canon professional SLR replaced by the EOS-1D X, the APS-H EOS-1D Mk IV, has 39 cross-type sensors, a major increase from the 19 of the Mk III. Of the 61 AF points of the EOS-1D X and 5D MkIII, 21 central points and 20 outer points are cross-type, and five central points are dual-cross-type (sensitive to diagonal lines in addition to horizontal and vertical).
Similarly, all nine AF points on later generations of the X0D series (beginning with the 40D and continuing through the current 60D) are cross-type sensors for higher accuracy, and the center sensor is dual-cross-type for even greater accuracy and sensitivity. In June 2012, the EOS 650D (Rebel T4i) became the first consumer-level Canon to receive this AF system.
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