Both Sony A3000 and Olympus E-M1 II have 20.0 MP resolution sensors but Sony A3000's sensor is APS-C (23.5 x 15.6 mm ) and Olympus E-M1 II's sensor is Four Thirds (17.4 x 13 mm ).
Since Sony A3000's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus E-M1 II.
One other difference between these two cameras that is worth mentioning is that Olympus E-M1 II'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 A3000 and E-M1 II sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A3000 and Olympus E-M1 II Cameras
As seen above, Sony A3000 has a 1.6x Larger sensor area than Olympus E-M1 II. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in 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. Sony A3000 and Olympus E-M1 II sensors have been tested by DxO and the results show that E-M1 II has a better overall score of 80, 2 points higher compared to A3000's score of 78.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A3000
78
23.7 bits
12.8 Evs
1068 ISO
Olympus E-M1 II
80
23.7 bits
12.8 Evs
1312 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
Sony A3000
or the
Olympus E-M1 II ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(APS-C versus Four Thirds),
so compare them at the same framing rather than the same focal length.
Put the same focal length on the smaller sensor and it will show less depth of
field, not more, because it also crops tighter. The calculator shows the
full frame equivalent focal length for each body so you can match the framing.
