Both Canon 1D X II and Pentax K-S2 have 20.0 MP resolution sensors but Canon 1D X II's sensor is Full frame (36 x 24 mm ) and Pentax K-S2's sensor is APS-C (23.5 x 15.6 mm ).
Since Canon 1D X II's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Pentax K-S2.
One other difference between these two cameras that is worth mentioning is that Pentax K-S2's sensor doesn't have an anti-alias (Low-Pass) filter. 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 1D X MII and K-S2 sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 1D X II and Pentax K-S2 Cameras
As seen above, Canon 1D X II has a 2.4x Larger sensor area than Pentax K-S2. 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 1D X II
or the
Pentax K-S2 ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(Full frame versus APS-C),
so compare them at the same framing rather than the same focal length.
Put the same focal length on the smaller sensor and it will show less depth of
field, not more, because it also crops tighter. The calculator shows the
full frame equivalent focal length for each body so you can match the framing.
