canon 70D when in ZONE AF why not all points lock onto focus, they jump around. Please explain!

[whitsitt1423]

When I have my Canon 70D in Zone AF, not all squares will show the little box inside, none show in red.  They seem to jump around and often wont rest on the part of the face I want it to *the eyes".  I know how to do one-shot but I'm wondering why the ZONE AF does this and how to get it to lock focus where I want it to.  Thanks!!  Such a seemingly simple thing but I have been researching it for hours with no progress!  thanks!!

[cicopo · Accepted solution]

As I understand it the AF system (using the available sensors which can be a single point, group or all of them) is trying to find the area with the best contrast to determine the distance & to lock onto it. That is ONE specific part of the scene. If you want it to be the eye you need to place an AF point on the eye using the little joystick or the center point by selecting just it. The AF system has no idea what you think is the most important part of the scene. It also can not focus on multiple areas of the scene, it focuses on one spot & DoF helps get other areas to appear in focus.

[whitsitt1423]

Thank you!

[TTMartin]

---

@whitsitt1423 wrote:

When I have my Canon 70D in Zone AF, not all squares will show the little box inside, none show in red.  They seem to jump around and often wont rest on the part of the face I want it to *the eyes".  I know how to do one-shot but I'm wondering why the ZONE AF does this and how to get it to lock focus where I want it to.  Thanks!!  Such a seemingly simple thing but I have been researching it for hours with no progress!  thanks!!

---

The following is from the 7D AF quick guide. I've only included the parts that apply to the 70D. To focus on the eyes you don't want to use 'Zone AF' you want to use single 'Manual AF Point' selection.

[kvbarkley]

They only blink red in low light, and only if you have that option turned on.