Both Sony A65 and Pentax K-3 have APS-C sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
One other difference between these two cameras that is worth mentioning is that Pentax K-3's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the A65 and K-3 sensor size comparison.
Sony A65 and Pentax K-3 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 A65 and Pentax K-3 sensors have been tested by DxO and the results show that K-3 has a better overall score of 80, 6 points higher compared to A65's score of 74.
Model |
Overall |
Color Depth |
Dynamic Range |
Low-light ISO |
Sony A65 |
74 |
23.4 bits |
12.6 Evs |
717 ISO |
Pentax K-3 |
80 |
23.7 bits |
13.4 Evs |
1216 ISO |