I recently bought a used 6D and it is a great camera for the price.
However, I noticed that it often struggles to autofocus when selecting all focus points. The lens goes back and forth and fails to hunt. It auto focuses on one point with no issues though, super fast and accurate.
I tested the lenses on another camera and autofocus works perfectly. So I can be sure the issue comes from the 6D body.
Does anyone know what might be wrong?
Edit: AF was set to ONE SHOT. The issue is that it can quickly and accurately focus on the target if I use any ONE of the focus points. However, if I choose to use all of the focus points, it struggles.
Yes ONE SHOT. And yes if I choose any of the focus points, it autofocuses perfectly.
But the thing autofocus should also work just fine if I choose all focus points
It should, it can, and it will. The camera’s AF system will default to focusing on the nearest subject to the camera. Present the camera with one nearby subject and a “distant” background, then the camera will lock focus on the nearby subject.
You have not described your shooting scenario. If the camera detects multiple subjects that are at or close to the same relative distance to the camera, the camera may not instantly lock onto the one subject that want. How should it decide which subject to focus on? It can focus on only one target at a time.
Sometimes, you have to help the camera acquire a subject on which to focus. Using a single AF point is typically how this is done. Most photographers use the Center AF point because it is most often the most sensitive AF point. Not all AF points are created equally, and this is especially true on the 6D.
All AF points were active for this shot. The camera had no problem quickly focusing on the closest subject to the camera.
The center AF point was used in this shot. One Shot AF was locked on the pumpkin just to the right of the center of the photo. I recomposed the shot after locking focus..
when you select a single focus point all the camera has to do is focus; you have done the work of selecting a suitable target. When you select multiple focus points the camera is programmed to select the closest object with sufficient contrast to achieve focus. Camera needs to do a lot more “thinking” and in some situations it may not find suitable targets right where the focus points are.