Both Sony A7S and Olympus E-620 have 12.0 MP resolution sensors but Sony A7S's sensor is Full frame (35.8 x 23.9 mm ) and Olympus E-620's sensor is Four Thirds (17.3 x 13 mm ).
Since Sony A7S'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-620.
Below you can see the A7S and E-620 sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A7S and Olympus E-620 Cameras
As seen above, Sony A7S has a 3.8x Larger sensor area than Olympus E-620. 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 A7S and Olympus E-620 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, A7S has scored 87, 32 points higher than E-620.
Model |
Overall |
Color Depth |
Dynamic Range |
Low-light ISO |
Sony A7S |
87 |
23.9 bits |
13.2 Evs |
3702 ISO |
Olympus E-620 |
55 |
21.3 bits |
10.3 Evs |
536 ISO |