Thanks for your thoughts. In the example situation, the subject was very brightly lit. This wasn't standard indoor light, it was a high-powered video light turned up to its maximum boost setting 3 feet from the subject. I'd be pretty concerned if the camera needs more light than that to be effective.
No, the camera has more than enough light there. Don't blame the camera, it is fine.
As for the AF fine tune, I did do a round of fine-tuning on the lens using a tuning chart. (this one to be exact:
https://www.amazon.ca/DSLRKIT-Focus...7&sprefix=auto+focus+tune+chart,aps,84&sr=8-2)
In that case, the lenses nailed focus every single time at about the same distance under the same conditions.
You don't need to tune the focus. This is a mirrorless camera, not a DSLR. It does not have a separate AF sensor like the DSLRs, it focuses directly from the image sensor. Look for problems in your use or configuration of the camera.
It seems to really struggle with people.
No, it does NOT struggle with people.
Something is to blame, either its me, the camera, the lenses, or the adapter. I want to blame that which is at fault so I can actually fix the problem. That said, the only NEW thing in the workflow is the camera+adapter, so it correlates. Its the thing that changed. If the problem is me that is the best-case scenario as it is the cheapest and easiest fix.
It would be easier to solve this if we were side by side, I bet you we would solve this in five minutes...

Maybe if you'd list every setting of your camera it would help also to find out what you do differently.
I really am not 100% convinced its the camera, its just all evidence points towards the camera or adapter atm. I want it to be user error, that's so easy to fix.
Here is the exact process and settings use to capture the photo in the example:
- Camera is locked off onto a tripod, and I even used a remote shutter release to ensure zero vibration.
- The subject is lit by a 200w video light at full power in a 50" Octobox, positioned similar to a beauty dish just above the subject's head feathering across the face. There is another 150w video light in another big octobox to frame right at about 30% power slightly behind the mode to create the kicker sheen.
- The camera settings were as follows: 1/400th F1.4 ISO 100 (manual mode). AF was on AF-S in focus priority mode and human subject detection. IBIS was turned off. Viewfinder live preview was turned off.
- To shoot the shutter button on the remote was depressed until the focus box turns green over the subject's eye, and then the photo is taken. (Note I also tested without the remote shutter in case it was to blame, no change)
This was repeated about 100 times (give or take) and the miss rate was around 80% as mentioned. It doesn't always miss the same, sometimes its on the ear, sometimes its on an eyelash, other times it's the hair. Tbh the feeling to me is that the camera gets "close" and then that's determined to be "good enough" so wherever it actually happens to be focused when it reaches "close enough" ends up being in focus.
I really do appreciate your time and help.