What's the deal with the X-T5 autofocus?

wansai wrote:

I was having problems until I made some setting changes (release on focus, turn OFF AF+MF). It's a bit arcane and seems unnecessary to have to do it, but once it's done, the AF & tracking is pretty good. Even saying that, I still find the Sony A7C to have better AF than the XT5. Or at least, even the lower Sony's are more reliable for AF.

The XT5 eye AF has a tendency to jump from left and right eye even when you specify which eye you want; like what happened in my daughter's photo here. The eye AF couldn't seem to decide which eye and even after I selected the eye I wanted, it jumped to the left right as I hit shutter release.

A scene like this would have been easy peasy with my Sony. Saying that, I do really like the XT5. You can work around this roughness. You can probably rightly argue that at this price bracket you shouldn't have to, but it is what it is; and as a whole the XT5 is a superb camera.

There is no EXEF data here so the remainder is conjecture.  But depending on your f- stop the DOF of the selected f-stop could make the difference in contrast between the eyes statistically equal.  In that case the choice between eyes is a coin toss.  That is an issue with the stochastic of the AF since that's how the decision is made.  Also I believe that Fuji (at least) don't know about the rest, uses a smaller f-stop than what might be selected during the tracking process to track focus.  Again DOF will then play a roll in determining the statistics that go to determine the AF.

In the image above (cute little girl by the way), the right side of her face is better lit.  Because of that there is more contrast on the right eye than the left.  Because of that the statistics coming from the right eye might be better than coming from the left which on the dark side of her face and more likely that not statistically the right eye will give better AF.   I would not be surprised that it would jump to the right eye and track it vs. the left eye which is a little more forward but dimly lit.