Both Olympus E-420 and Panasonic GH5S have Four Thirds sized 10.0 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 Panasonic GH5S'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 E-420 and GH5S sensor size comparison.
Sensor Size and Resolution Comparison image of Olympus E-420 and Panasonic GH5S Cameras
Olympus E-420 and Panasonic GH5S 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
Olympus E-420
or the
Panasonic GH5S ,
including hyperfocal distance.
