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. [Read more…]