Originally posted by Fogel70 Isn't this just using fancier words saying the same thing? If GH2 can't lock focus within a second it has repeatedly done 120 steps of checking increased/decreased contrast and shifting focus after each check.
No, it does not mean that there is one focus shift(and a stop) of the lens after each frame check. That would be like running a 100m race within your lane, but stopping every second to check that you're in your lane!!!!! You can do both at the same time: Run continuously AND check to make sure you're in your own lane while doing it!!!!
For starters, according to figures, the GH2 can focus lock in 0.1 seconds not ONE second. You have made the mistake of thinking that you need to COMPLETE all 120 frames before it will focus lock. The rate of 120fps vs 60 fps means that the check speed is twice as fast.
It works like this.
It does a contrast check, then moves the lens focus. Let's say it's been moving the lens CONTINUOUSLY for 0.07 sec, in which time it's done 8 frame checks.
It's found that the contrast increased on frames 1,2,3,4,5,7, but decreased on frame 8. So far it has made just one focus "step" but has been monitoring the contrast continuously.
The focusing changes direction (step 2). It finds on frame 9,10,11(with smaller focus movement speed, for more precision) in it increases contrast, but on frame 12, it decreases. Finally(the processor remembering the increases and decreases in contrast), it changes the focus direction again(step 3), and on frame 13 it increases contrast and on frame 14 it locks focus.
The total time for focus lock is 0.117 seconds, with a total of 3 focus steps, and NOT 14 focus steps.
In this case, if both the GH2 & the GH1 need 14 frames to focus lock, then while the GH2 locks in just over 0.1 seconds, the G1 would take more than 0.2 seconds.
I can see that you don't want to believe how it works, and that PDAF lenses can work on CDAF cameras with a suitable adapter. Smart electronics in the adapter can "trick" the camera into thinkng that it has a CDAF lens attached. The electronics then provides a suitable electronic control system to drive the focus motor, and feeds back the appropriate data to the camera to make it appear that it's a CDAF lens.