My 2 cents : A7 vs A7R focus

Started Dec 13, 2013 | Discussions thread
UnderDriven Senior Member • Posts: 1,089
Re: Where's the authoritative source?

sroute wrote:

What I'm trying to get to the bottom of is exactly how the A7 camera's hybrid autofocus system actually works, using facts from the source, not speculation.

I don't think anyone knows, other than Sony. The A7 has 117 PDAF points in the center, and it is listed as having 25 CDAF "points" which are shown as a 5x5 matrix over the whole sensor (see image). However, the size of the focus area seems to be controllable, so what do these 25 CDAF "points" really mean? It might be an interesting experiment to choose an AF area at the edge of the image (outside the PDAF sensor area, if this is possible) and see if the performance is any different (speed and accuracy). The camera should be forced to use only CDAF outside the PDAF area. But I don't know if it is possible to choose an AF area that close to the edge, despite Sony's diagram of the AF system on the A7:

Also, if speed is the main priority of the A7 then Sony may have implemented an algorithm that (1) uses fewer pixels to initially find high contrast edges, and/or (2) has a 'timeout' on achieving optimal focus.  No one really knows, and it will take thorough testing to even develop an idea about what Sony is doing (if Sony chooses not to reveal the exact algorithm).  I am not sure I would trust some of these early reports because people may not be familiar with the system...

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