Both Pentax K-7 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 K-7 and K20D sensor size comparison.
Sensor Size and Resolution Comparison image of Pentax K-7 and Pentax K20D Cameras
Pentax K-7 and Pentax K20D 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. Pentax K-7 and Pentax K20D sensors have been tested by DxO and the results show that K20D has a better overall score of 65, 4 points higher compared to K-7's score of 61.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Pentax K-7
61
22.6 bits
10.6 Evs
536 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
Pentax K-7
or the
Pentax K20D ,
including hyperfocal distance.
