Not many people still use the Canon EOS 6D mk. II, a 2017 camera in the big 2026. Fewer still use it with vintage manual lenses that are old enough to vote.

The 6Dii still uses an optical viewfinder. Nothing wrong with it, really, but you can't really zoom in to help with focusing. It also does not have the focusing screen that cameras designed to use these lenses have.

The only way out, therefore, is Live View, which does, in fact, have a digital zoom to help with focusing.

This is fine, but when using lenses with ridiculously short depth of field, like my NIKKOR 180/2.8 ED* AI-s, I always seem to misfocus, no matter how sure I am when using LV.

Reference "Sharpness":

It feels 50/50 most of the time, which is not ideal.

The solution?

Silent LV Shooting

It didn't make sense that, at 1/500s, there would still be enough camera shake to cause the apparent lack of focus.

Specifically, mode 1 silent shooting

Apparently, it was the shutter movement ("shutter slap") that made the camera shift just enough for the focus to shift. According to the Depth of Field calculator from Photopills, the depth of field for a 180mm f/2.8 lens at minimum focusing distance (approx. 2m) is just 2cm! No wonder any slight shifts cause the image to be out of focus.

Lesson: RTFM! Even with things like cameras!