Canon 5D MkIII focusing

[xh28]

Hi

I do quite a lot of running photography with my 5D and L Series 24-105mm lens and most of the time it is great but occasionally (and certainly more often than I would like) it just doesn't focus properly or quickly enough.

See attached image using LR focus point plugin.

Welcome suggestions as to why this is.

 

[Maximilian]

I do a lot of football/soccer shots of my children. So even more dynamic sports and changes of movement than running.
I haven't played around with the 5D3 AF system. so I am mostly in factory settings.
The only thing I do is to switch to AF "Case 4" as well as AI Servo and 8 point expansion as you do.
Of course I don't get 100 % sharp and especially when subject is close to me (less than your displayed 8 m) the AF struggles.
But with everything else I am pleased.

So I have not much help for you but...
In your pic I can see a second runner with green shirt and orange shoes directly behind the black one.
His shoulders seem to be in focus.
Maybe the AF was locked on that one although you triede to get the black one in focus.
Depends on how the situation was.

 

[xh28]

I do a lot of football/soccer shots of my children. So even more dynamic sports and changes of movement than running.
I haven't played around with the 5D3 AF system. so I am mostly in factory settings.
The only thing I do is to switch to AF "Case 4" as well as AI Servo and 8 point expansion as you do.
Of course I don't get 100 % sharp and especially when subject is close to me (less than your displayed 8 m) the AF struggles.
But with everything else I am pleased.

So I have not much help for you but...
In your pic I can see a second runner with green shirt and orange shoes directly behind the black one.
His shoulders seem to be in focus.
Maybe the AF was locked on that one although you triede to get the black one in focus.
Depends on how the situation was.

Thanks for the reply. One of the things I have been reading about is the AF cases. I have been on the factory setting so case 1 but I will give case 4 a go to see if it helps. I am interested in your comment about the AF struggling at close range. I will experiment with that as well.

Thanks for your time.

 

[Maximilian]

I am interested in your comment about the AF struggling at close range.

The reason for that is quite easy:
If someone moves with e.g. 15 km/h and is closer to you than the relative movement angle at shorter distances is wider and therefor the AF has to work harder and faster.