I have 70D and yesterday I have encountered this problem with central focus point.
Sigma 18-35 1.8 lens:
Central point at 1.8, more than 50% miss
Other points at 1.8, less than 10% miss
I'm very disappointed.
How have you set the AF menu options up?
Which AF Point mode are you using?
And AI Servo? AI Focus? One Shot?
I ask because there's a recurring theme in these discussions of user error...
Here's the thing. All cameras AF (and meter) wide open: so if every single time anyone presses the shutter button your lens is wide open, how is this "problem" not manifesting at any aperture?
Yet the people who reckon they're victims seem pretty clear that it's "only" at maximum aperture as they've set it. How can that be?
It strongly suggests a flawed testing regime, the normal impact on DoF of shooting wide open, and unrealistic/uninformed expectations. I've seen no evidence to support any claims that there's a ubiquitous design/production flaw in the 70D.
Some obviously faulty individual cameras? Yep. Lots of user error? Yep. An inherent flaw in the camera. Nope...
I have checked few times - One shot focus, near and far distance. Liveview is fine, other focus points are fine, central focus point - crap.
And the DOF on crop 18 1.8 few meters away is not a hair.
Of course I will do more tests with other lenses, but for me this is strange issue, and I bought 70D to replace my 60D for better focus...
I'm CPS member and I'm awaiting their answer what are the possibilities.
P.S. Totally agree about the lack of fast lenses for most of the 70D owners, also many of them are probably using Auto AF, AF zones or Liveview.