GH4 Abnormally slow AF

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divide

Well-known member
Hi,

I just went to the camera store today to test the GH4 AF, and I was really surprised by the poor performance I got.
The GH4 had the 12-35 f2.8 (mostly using 25-35@2.8), AFC, and I tried several focus mode (zone, point, multizone...) in movie mode.
Going from one object to another (either by panning the camera or touching a different zone) performed ok, but it really had a hard time by just moving to and away specific object.
For instance I pointed the camera at a sheet well lit with a lot of text and graphics, waited for the focus, then moved back slowly with the sheet still in the focus zone: for a few second it was able to keep the focus on the sheet, but then gave up, I was in total blur for at least 10 second, and the camera not even trying to focus ! Not even sure it would have tried to focus if I didn't halfpressed the photo button intentionally.
It was not a one time failure, I was able to repro that non-autofocus behaviour several time.

Did I do anything wrong ? Have you experienced similar behaviour ? Was the camera defective ?
 
The AF performance is not that fast in 4K, especially indoors and in low light. At 4K, I use my manual focus.
It's better at 1080, though.
 
I was using 1080p50 so there's no reason it would be slow in my test. Like, super super slow, to the point of not even trying to focus in certain condition.
 
It is good that AF is slow, it could be otherwise too nervous to focus everything that moves. I still would like to have adjustable speed for AF. Fast for sports and kids, slow for normal use. You can help AF with half press or touch.
 
It is good if it is a little slow. It is super bad if it doesn't even try to focus when moving away from a subject.
Halfpressing to refocus is not an option, in this case it does a quick rescan and run super fast on my target focus point, not looking video at all.
Regarding my first post, did anyone experience such a behavior with the camera not trying to focus when moving away from a subject, even in 1080p50/60,AFC,good lighting, good details in the focus zone?
 
Did you have continuous auto focus on in the menu or just simply have the focus lever on AFC? The switch doesn't change AF modes for video mode, just stills (I actually really wish it did so I didn't have to dig through the menu to turn continuous AF on and off). If that menu setting is not on it won't try to refocus without a shutter button press.

Also, I do find picture profile plays a role. Less contrasted modes like Cine D seem to work worse. But 1080, whether 24 or 60, has been very good usually for me regardless, so that makes me think it might be the former.
 
divide said:
It is good if it is a little slow. It is super bad if it doesn't even try to focus when moving away from a subject.
Halfpressing to refocus is not an option, in this case it does a quick rescan and run super fast on my target focus point, not looking video at all.
Regarding my first post, did anyone experience such a behavior with the camera not trying to focus when moving away from a subject, even in 1080p50/60,AFC,good lighting, good details in the focus zone?
Click to expand...

GH4 AF in video is sometimes very "sleepy" and forgets to follow subjects in focus box or goes to wrong direction and then looses the situation. AF fails easily also when there is high contrast background and low contrast subject.

Yes the half press leeds to quick ugly looking focus reset. You can have slower looking focus "wake up" by using touch focus. You can set it so that you can use touch pad focus even when using EVF. If you use "offset" function the focus box is not moving when you touch the right side of the screen with your thumb. It only refocuses slowly.
 
FWIW: I finally bought a GH4 (fw 2.0)+12-35 (fw 1.2) -the more I use it, the more I love it!- and so I could experiment a little more with the AF behavior.
I was disappointed to see the same sleepy behavior I saw in the camera store...
...until I activated the "record" button. And then it was a whole different story ! When recording (1080p24), the camera never forget to pull the focus as required. It has nothing to do with the behavior I see when the camera is not recording.
I don't understand why this difference in AF behavior, but I'm very happy it reacts properly when recording, I never need to half-press to focus while things happen and that's what matters most :)
 
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