Both Olympus E-520 and Olympus E-420 have Four Thirds sized 10.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the E-520 and E-420 sensor size comparison.
Sensor Size and Resolution Comparison image of Olympus E-520 and Olympus E-420 Cameras
Olympus E-520 and Olympus E-420 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.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Olympus E-520 and Olympus E-420 sensors have been tested by DxO and the results show that E-420 has a better overall score of 56, 1 points higher compared to E-520's score of 55.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Olympus E-520
55
21.4 bits
10.4 Evs
548 ISO
Olympus E-420
56
21.5 bits
10.4 Evs
527 ISO
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-520
or the
Olympus E-420 ,
including hyperfocal distance.
