New (to me) EF 85mm 1.2 picks it's own focus point

[mattplatts]

I recently picked up a used EF 85mm 1.2 L II to use primarily on my R6 mk2. I've found that it tends to focus somewhere other than where I point it. When I use Spot or 1-Point AF, it seems to be looking around to find maybe the closest object, or maybe the highest-contrast object rather than what I have the focus point aimed at. It doesn't matter how much light there is - this can be in broad daylight or in low light.

As an example, taking a picture of a plant pot - I put the AF mark on the leaf or bloom that I would like in-focus, but the camera focuses on another leaf or bloom. I've tried opening up the AF options to larger areas, and that just broadens where it looks... and rarely focuses on what I intend. My expectation with Spot or 1-Point AF is for the camera to focus on that spot each and every time, assuming there is adequate light, which there is.

I've tried two different adapter rings, and that doesn't make a difference. I've also tried the lens on my daughter's Rebel Ti, and it works better there. That camera only has a few focus points, and the lens focuses on the point I select each and every time. Could there be an issue with the lens, or maybe this EF lens just doesn't talk well to an RF camera's new focusing system? I can send the lens back and try another one, but I thought I'd check to see if this is a common issue for this lens (or camera settings?) before sending it back.

Hoping that the community can clue me in on what I might be doing wrong!

[jrhoffman75]

Expanding on what others have posted, the camera will attempt to focus on the closest object to the camera with sufficient contrast. Placing the focus point on a green leaf or flower petal may not have sufficient contrast. Similarly a green grass lawn may not have sufficient contrast. 

[ebiggs1]

"Expanding on what others have posted, the camera will attempt to focus on the closest object to the camera with sufficient contrast."

The last part of that is very important.

[mattplatts]

Problem solved, and yes, it was user error. What I didn't realize when setting up back button focus is that by selecting "AF on detected subject" for my primary AF button because I predominantly shoot sports lately, that makes the camera always look for a subject... like it's searching for people (in my case usually), animals, etc. I thought that by selecting my AF Area as 1-point AF or Spot AF, that would override the "subject" part. It does not. Once I changed that back button focus option to simply "Metering and AF start", the camera now focuses on just the single point or spot that I prefer when using this lens for shooting plants, flowers, etc. I am now able to pick the exact leaf, flower petal, etc, that I want to focus on and the camera does it without question.

With this realization, I've saved custom function C1 so that my primary BBF button is a single point, and left C2 and C3 (indoor sports and outdoor sports) so that my primary BBF button looks for the subject.

Thanks for all the suggestions that ultimately pointed me to the cause. Now I have a smile on my face when I go out to use this "new to me" lens!