Both Leica M EV1 and Leica Q3 have Full frame sized 60.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
One other difference between these two cameras that is worth mentioning is that Leica Q3's sensor doesn't have an 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 M EV1 and Q3 sensor size comparison.
Sensor Size and Resolution Comparison image of Leica M EV1 and Leica Q3 Cameras
Leica M EV1 and Leica Q3 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. On the other hand, since Leica Q3 has 29% larger pixel area (18.49µm 2 vs 14.33µm 2 ) compared to Leica M EV1, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.
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
Leica M EV1
or the
Leica Q3 ,
including hyperfocal distance.
