Houses at a few hundred feet shot with the over-under camera orientation
with medium-long teles sometimes show identical detail in the in-focus
areas, and identical focus point, yet the out-of-focus trees behind the
houses will show a different character in the two like images. I would
guess that this may indicate slight element decentering (wide-angle DOF
probably conceals similar effects, but wide-angles and zooms are more
likely to show gross inequalities in the frame-couple edges indicating
misalignment).