Sorry for the late reply. What we’ve found is that they’re all close but not identical. Our system has a point LIDAR pointed at the ground and then uses that to drive the focal distance for the lens (as well as input for some other sensor fusion stuff). We generally run the lenses wide open (f/2.0 or f/2.8). Mapping step counts to distance would get us close, but unless we did calibration for each individual lens it wasn’t close enough to get the focus tack sharp. When you’re looking at the focal distance in your EXIF metadata you’re probably not validating whether that 2.4m distance to the subject was actually 2.3m and for the vast majority of cases the absolute accuracy of it doesn’t matter. Same with the distance markers on the focus ring… you’re not setting the focus within a few cm based on those marks, just getting it close enough that you can do closed-loop focusing with an eyeball in the loop.

Once we did the per-lens calibration curve we didn’t have to do it again. I’m assuming the small differences are just manufacturing tolerance and they’re relying on the focus/phase sensors to get it the rest of the way.