I tested the Tokina atx-m 85mm f1.8 FE on a Sony A7R III and they got most subjects sharp very quickly. The Eye AF also worked well when set to Human or Animal (with my dog).
Although I was able to focus on quite fast-moving subjects like teasels blowing in the wind, the continuous focusing system doesn’t seem quite as snappy as when there’s a native lens mounted on the camera.
The sharpness is very good at the centre of the frame throughout the whole aperture range although there’s a slight improvement when stepping down from f/1.8. Also, if you examine images at 100% on screen, the effect of diffraction becomes just visible at f/11 and more so at f/16 – it’s nothing to worry about though.
If you check the corners of images shot at f/1.8 at 100%, you’ll notice some softening, but it’s not likely to be an issue for portraiture. Closing down to f/2.2 sharpens things and by f/4 to detail looks good across the whole frame.
There’s also mild vignetting at f/1.8 but it’s negligible at f/4.
In summary, I wouldn’t hesitate to use any of the Tokina atx-m 85mm f1.8 FE’s aperture settings.
If you hunt around your images at 100% on a computer screen you may find some chromatic aberration, but it’s not problematic and can be easily addressed during the raw file processing.
You may also notice slight pincushion distortion, but it’s not excessive or something that’s worth worrying about for most uses of the lens.