Both Sony A57 and Olympus E-M1 have 16.0 MP resolution sensors but Sony A57's sensor is APS-C (23.5 x 15.6 mm ) and Olympus E-M1's sensor is Four Thirds (17.3 x 13 mm ).
Since Sony A57'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.
Below you can see the A57 and E-M1 sensor size comparison.
As seen above, Sony A57 has a 1.6x Larger sensor area than Olympus E-M1. 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 A57 and Olympus E-M1 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, A57 has scored 75, 2 points higher than E-M1.
Model |
Overall |
Color Depth |
Dynamic Range |
Low-light ISO |
Sony A57 |
75 |
23.4 bits |
13.0 Evs |
785 ISO |
Olympus E-M1 |
73 |
23.0 bits |
12.7 Evs |
757 ISO |