On July 2010, 21, Fujifilm introduced the F300EXR with a then new kind of AF, called "Hybrid AF" by Fuji. It makes use of the fact that the microlens which modern cameras have in front of every pixel on the sensor, creates a directional dependency of brightness distribution on the light sensitive pixel surface.

So, Fuji masked one half in some, the other half in some other of the pixels (but modified only a few pixels in total). It could therefore create two signals (low resolution images) from the modified pixels which are used to determine a phase shift between the two. The modified pixels aren't used to take the image itself.

Canon took this idea, sat down for a few hours and thought: "well, what if we didn't mask one half of a pixel but split it into two and only reading one at a time?" Here is what it looks like:

Obviously, Canon pays better graphics designers than Fuji. Other than that, the two illustrations look pretty similiar. So maybe, it is no surprise that it took them exactly 12 working days to write this idea down and file another patent on 2010, August 9, a Monday ... 2 busy weeks. The idea is obvious. But only Canon reacted quick enough to make it a patent. And only Canon was brave enough to actually double the pixel count in a real product. It took them 3 years to do. I applaud Canon for what I think is a business master piece.

Yes, it really is a new type of AF. The idea is quite simple and is the same as with the Hybrid AF. But executed with brute force. And what you get in return, wow!

Unlike PDAF and Hybrid AF, CDAF can make use of all available light falling into the lens. This is a massive advantage. Sadly, it is offset by a large number of measurements it must take in order to maximize contrast. Especially as many vendors don't apply sophisticated algorithms to minimize the number of measurement steps. On the other hand, PDAF and even more Hybrid AF, only use a fraction of available light for their measurement.

The new MPAF is the first kind of AF which does both: use all light and minimize the number of measurements. Canon's first installation with its focus on continuous movie focusing may not tell the full story yet, but I am convinced that eventually, MPAF will blow all other kinds of AF out of the water. In terms of speed, tracking ability, accuracy, and low light capabilities.

The MPAF is a breakthrough here: it eventually allows the high end cameras to drive innovation rather than play the conservative watcher. This redefines the rules and will transform the industry.

http://falklumo.blogspot.ru/2013/07/comment-why-new-dual-pixel-af-will.html