Both Sony A57 and Pentax K-500 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 A57 and K-500 sensor size comparison.
Sony A57 and Pentax K-500 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the 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 Pentax K-500 sensors have been tested by DxO and the results show that K-500 has a better overall score of 79, 4 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 |
Pentax K-500 |
79 |
23.7 bits |
13.1 Evs |
1087 ISO |