Sigma DP3 Merrill has a
15.0MP APS-C (24 x 16 mm ) sized CMOS (Foveon X3) sensor and features Dual TRUE II engine processor. On the other hand, Nikon D5100 has a
16.0MP APS-C (23.6 x 15.7 mm ) sized CMOS sensor and features Expeed 2 processor.
Below you can see the DP3 Merrill and D5100 sensor size comparison.
Sensor Size and Resolution Comparison image of Sigma DP3 Merrill and Nikon D5100 Cameras
Sigma DP3 Merrill and Nikon D5100 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.
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
Sigma DP3 Merrill
or the
Nikon D5100 ,
including hyperfocal distance.