10 months ago
IR interviewed Canon in Japan and the US with focus on the 70D. I found the comments on the dual PDAF interesting.
"In most scenes, it will not prove as accurate to the degree of accuracy that we would like, which is why we hand it over to the contrast detection AF to ensure proper accuracy and precision. This also relates to the Dual Pixel CMOS AF that's incorporated in the 70D, and that uses contrast detection to ensure proper accuracy."
"Note, though, that I said phase detect operation, as that's only part of the process the EOS 70D uses in live view AF, at least for still-image focusing. Part of the reason the 70D's Dual Pixel AF isn't as fast as the conventional separate-sensor approach is that the 70D only uses Dual Pixel technology to achieve rough, initial focus; it then switches to contrast-detect focusing to check focus accuracy and, if necessary, fine-tune focus. (The other part is that data most likely can be read out from the dedicated AF sensor more quickly.) This means that the slightly lesser accuracy of Dual Pixel CMOS AF doesn't affect ultimate focus accuracy, just the speed with which you achieve it.
When it comes to video focusing, though, even Full HD (1,920 x 1,080 pixel) resolution is so much lower than the 70D's 20-megapixel still image resolution that the slightly lower PDAF accuracy of the Dual Pixel CMOS AF system matters not a bit, while its ability to focus smoothly and continuously at apertures down to f/11 is a huge benefit."