Focusing issues on live view - Nikon D750 w/ AF-S NIKKOR 24-70mm f/2.8G ED

by Lisan   Last Updated August 13, 2019 18:18 PM

On a heavily used Nikon D750 w/ AF-S NIKKOR 24-70mm f/2.8G ED:

When using live vision, ussualy while holding the camera up over my head, autofocus focuses nowhere. This happens right after having shooted a correctly focused photograph using viewfinder, with slight subject distance variation.

When doing so, I hardly ever want a shallow DoF, as I'm focusing on groups of people, so F-number is always between F5.6 and F16. Focusing mode is always AF-C and center point, and I don't use shutter button focusing, I use only dedicated AF-ON button focusing. So it should just focus at center of image as I press AF-ON button, and keep this focus distance until I shoot.

In most notorious cases, it seems to be getting stuck at its shorter focusing distance:

(f/7.1, 1/80s, ISO-4000, I couldn't look at the screen while focusing, but it should undoubtly have focused some of the people in the central area, or at least the wall behind them) enter image description here

At some other situations, it fails to focus the central situation, setting focus on closer, peripheral subjects (as if I was using multiple point AF selection, what I am NOT doing):

(f/7.1, 1/125s, ISO-5000, I pressed AF-ON button while pointing to people speaking at the table) enter image description here

Is this caused by a fail, A D750 common issue, or a mispractice?

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