Both Canon 50D and Sigma DP3 Merrill 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 DP3 Merrill sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 50D and Sigma DP3 Merrill Cameras
As seen above, Sigma DP3 Merrill has a 1.2x Larger sensor area than Canon 50D. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
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
Sigma DP3 Merrill ,
including hyperfocal distance.
