Both Pentax K20D and Canon 50D 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 K20D and 50D sensor size comparison.
Sensor Size and Resolution Comparison image of Pentax K20D and Canon 50D Cameras
Pentax K20D and Canon 50D 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
Both Pentax K20D and Canon 50D sensors have been tested by DxoMark. DxoMark 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. Of the two cameras that we are comparing, K20D has scored 65, 2 points higher than 50D.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Pentax K20D
65
22.9 bits
11.1 Evs
639 ISO
Canon 50D
63
21.8 bits
11.4 Evs
696 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
Pentax K20D
or the
Canon 50D ,
including hyperfocal distance.
