x-ray
Veteran
Good luck.
My last portrait session with my MF Nikkor 85mm f/1.8 Ai used at f/2.8, using the original focusing screen, the DK-17M lupe, the green dot indicator and being extra careful about my focusing ended up with 1 photo out of 10 which was focused like I intended to (on my model's eyeballs).
Ive found through a great deal of experience that most subjects / people can't hold still enough for shooting at very wide apertures. The only have to move a quarter of an inch or so to shift focus to a different part of the face. Also if you're hand holding you're moving slightly too.
The only AF lens I use routinely on my DF is an 85 f1.4 D. I use the Df in continuous servo mode and manually select a focus point I put on the closest eye to the camera. I shoot at wider apertures with no problem and shoot commercial portrait sessions weekly. Today I have 5 physicians I'll shoot for one of my accounts and over the course of a year I probably shoot over 100 sessions. I won't say I get 100% sharp but it's over 90%.
Manual focus at close distance would present new challenges with a subject even barely moving. People rarely can hold perfectly still for shallow dof portraits.

