Sony A57 has a
16.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor . 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 A57 and E-M1 II sensor size comparison.
As seen above, Sony A57 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 A57 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, 5 points higher compared to A57's score of 75.
Model |
Overall |
Color Depth |
Dynamic Range |
Low-light ISO |
Sony A57 |
75 |
23.4 bits |
13.0 Evs |
785 ISO |
Olympus E-M1 II |
80 |
23.7 bits |
12.8 Evs |
1312 ISO |