Both Canon 50D and Pentax K20D have APS-C sized 15.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the 50D and K20D sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 50D and Pentax K20D Cameras
Canon 50D and Pentax K20D 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. Canon 50D and Pentax K20D sensors have been tested by DxO and the results show that K20D has a better overall score of 65, 2 points higher compared to 50D's score of 63.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Canon 50D
63
21.8 bits
11.4 Evs
696 ISO
Pentax K20D
65
22.9 bits
11.1 Evs
639 ISO
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Canon 50D
or the
Pentax K20D ,
including hyperfocal distance.
