So, dumb question... why does it say "focus distance between 81.91m and 559.79m"? Doesn't it know much more precisely than that what distance the lens is focused at?
Thats a good question.
The metadata in the file isn't very specific with focus distances (at least for larger values anyway). Some years ago I had an idea to write an image processing application that used the focus distance but found that the data just wasn't accurate enough for the job.
I don't know if the camera actually knows what the focus distance is. Part of me suspects it's just changing focus on the lens until it gets the image sharp (or rather "aligned", for phase AF).