One of the most crippling features in many DSLR cameras (like the Canon Rebel T2i above) is the poor autofocus performance in both live view and video modes. While mirrorless cameras like the Panasonic GH1 and Samsung NX10 do a decent job of using contrast-detection AF methods, DSLR manufacturers like Canon and Nikon have done a poor job in making it work. Sony, to its credit, has implemented an effective live view design with fast autofocus by placing a secondary live view sensor in the viewfinder, which allows the standard phase difference AF sensor to function normally. But, still, it’s not a true “live view” of what the sensor will produce. Plus, Sony’s design won’t work with video.
Of course, most pros and serious amateurs understand the benefit and efficiency of using the fast, phase difference AF method that results from using the viewfinder. However, that doesn’t stop entry-level and enthusiast photographers from complaining about the poor live view and lack of video autofocus in their sub-$1000 DSLRs. Additionally, there are certainly situations where an accurate and quick live view or video autofocus mode are desired among photographers of all skill levels and backgrounds.
Canon may very well have the answer: Put the fast, phase difference AF sensors in pixels on the main image sensor.