Sigma Quattro has a
29.0MP APS-C (23.5 x 15.6 mm ) sized CMOS (Foveon X3) sensor and features Dual TRUE III processor. On the other hand, Pentax K-3 III has a
26.0MP APS-C (23 x 15.5 mm ) sized BSI-CMOS sensor and features PRIME V processor.
Another similarity between these two cameras is that both Pentax K-3 III and Sigma Quattro sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the Quattro and K-3 III sensor size comparison.
Sensor Size and Resolution Comparison image of Sigma Quattro and Pentax K-3 III Cameras
Sigma Quattro and Pentax K-3 III 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 Quattro
or the
Pentax K-3 III ,
including hyperfocal distance.
