The Rebel T4i is the first Canon DSLR to feature full-time AF in video mode. The past Canon DSLRs have featured the ability to force an AF confirmation using a slow and clunky contrast-detect method, which was simply unusable during video capture. Another AF confirmation option has been to use the cameras' phase detection sensors; however, this caused a blackout during live view thanks to the mirror flipping down in front of the image sensor.
The folks over at Chipworks [via Image Sensors World] tore down a Rebel T4i to get a look at the image sensor and reveal phase detection sensors mixed among the pixels. This is something that Canon has been cooking on for a while. (Note this patent application that I discussed back in 2010.)
And while we've seen this concept implemented in prior cameras (notably the Fuji F300EXR point and shoot camera and Nikon 1 Series), Canon has gone about it in a technically different way to make it effective for DSLRs.
…we can see that unlike the Aptina sensor Canon is using a somewhat irregular pixel pattern for phase detection versus Aptina that used a set of regular lines. -Chipworks
Given the presence of this sensor in the Rebel T4i, you can bet that a similar sensor design with built-in phase detection pixels will find its way into the upcoming Canon mirrorless camera. This should really boost the reliability and speed of the mirrorless models' AF. (I don't really give much credence to Nikon's very consumer-ish entry into the mirrorless market with its 1 Series models and the small 2.7x crop sensors.)
Hopefully, Canon's design will lead to the ability to select much smaller AF points in live view systems. For me, those large AF "points" on mirrorless cameras have been the primary cause for me to pick up my…
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