Both Sony A55 and Pentax K-50 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 K-50 sensor size comparison.
Sony A55 and Pentax K-50 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 A55 and Pentax K-50 sensors have been tested by DxO and the results show that K-50 has a better overall score of 79, 6 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 |
Pentax K-50 |
79 |
23.7 bits |
13.0 Evs |
1120 ISO |