Both Sony A55 and Sony A57 have APS-C sized 16.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the A55 and A57 sensor size comparison.
Sony A55 and Sony A57 have the same sensor sizes so they will provide same level of control over the depth of field when used with 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 A55 and Sony A57 sensors have been tested by DxO and the results show that A57 has a better overall score of 75, 2 points higher compared to A55's score of 73.
Model |
Overall |
Color Depth |
Dynamic Range |
Low-light ISO |
Sony A55 |
73 |
23.0 bits |
12.4 Evs |
816 ISO |
Sony A57 |
75 |
23.4 bits |
13.0 Evs |
785 ISO |