Both Olympus E-M1 and Sony A580 have 16.0 MP resolution sensors but Olympus E-M1's sensor is Four Thirds (17.3 x 13 mm ) and Sony A580's sensor is APS-C (23.5 x 15.6 mm ).
Since Sony A580'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 E-M1 and A580 sensor size comparison.
As seen above, Sony A580 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
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-M1 and Sony A580 sensors have been tested by DxO and the results show that A580 has a better overall score of 80, 7 points higher compared to E-M1's score of 73.
Model |
Overall |
Color Depth |
Dynamic Range |
Low-light ISO |
Olympus E-M1 |
73 |
23.0 bits |
12.7 Evs |
757 ISO |
Sony A580 |
80 |
23.8 bits |
13.3 Evs |
1121 ISO |