Both Fujifilm X100S and Leica X Vario have APS-C sized 16.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Another difference between these two cameras is that Fujifilm X100S's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the X100S and X Vario sensor size comparison.
Sensor Size and Resolution Comparison image of Fujifilm X100S and Leica X Vario Cameras
Fujifilm X100S and Leica X Vario have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Fujifilm X100S
or the
Leica X Vario ,
including hyperfocal distance.
