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. [click to continue…]
In the recent post about the Sony A77 prototype camera on display at CP+, Chris left a comment asking about the price of the new camera, which is due to be released later this year.
So far, Sony hasn’t revealed the price point for this new camera. However, we do know a few things about the A700 successor. [click to continue…]
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.
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A patent application filed by Canon was recently published by the USPTO (App. No. 12/188,385) that may give us some insight as to how Canon will solve the abysmal autofocus performance of Canon’s Live View mode. If you are unfamiliar about how Canon’s Live View AF system currently works (or doesn’t work), you can read my prior rant in Photography Bay’s Canon Rebel XSi Review. For some insight on how Live View AF should work, see the Sony A350 Review.
Nothing works faster for DSLR autofocus systems than the tried and true phase-difference method. If you don’t know what phase-difference AF means, the you can read about it on Wikipedia; however, it’s not essential to understand all the technical details to get excited about Canon’s new patent.
The fundamental problem with making phase-difference autofocus work in a Live View mode is that the AF sensor receives light from the mirror, which also reflects light up into the pentaprism for the optical viewfinder. When you press the shutter button, the mirror flips up and you get a brief moment of black out in the view finder while the shutter opens and exposes the image sensor to the light from the lens. [click to continue…]