For some reason, possibly operator error, my X-T50 stops the lens down to autofocus. Happens with three lenses, OEM and third-party, all bought new (haven't tried any others). If I set the aperture to (say) f16, when I press the back button to AF, the viewfinder gets very dark, and the camera misses focus. I can watch it hunting, and it occasionally finds focus and then loses it. This appears to have happened today, even at f5.6. Has anyone else had this happen? Are there settings I am missing? (There always seem to be. 🙂)