Sony A7 has a
24.0MP Full frame (35.8 x 23.9 mm ) sized CMOS sensor and features Bionz X processor. On the other hand, Olympus E-M1 II has a
20.0MP Four Thirds (17.4 x 13 mm ) sized CMOS sensor and features TruePic VIII processor.
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 A7 and E-M1 II sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A7 and Olympus E-M1 II Cameras
As seen above, Sony A7 has a 3.8x 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
Both Sony A7 and Olympus E-M1 II sensors have been tested by DxoMark. DxoMark 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. Of the two cameras that we are comparing, A7 has scored 90, 10 points higher than E-M1 II.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A7
90
24.8 bits
14.2 Evs
2248 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 A7
or the
Olympus E-M1 II ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(Full frame 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.
