X100 lens has a flat field of focus.
I did a quick test on a tripod to check the focus accuracy at f2 across the plain of focus. I was very impressed to see that there was no perceptable differerence between focusing with the focus box set in the centre of the frame to focusing with it positioned to either side of the frame. This is good to know, as it negates the need to move the focus box to either edge when the main subject is off-centre. One only needs to focus and re-compose, even at f2 and be assured that the focus will not shift. (Samsung 30mm f2 lens or 20mm f2.8 lens cannot be used this way, I have discovered).