Leica Q3 Monochrom has a
60.0MP Full frame (36 x 24 mm ) sized BSI-CMOS sensor and features Maestro IV processor. On the other hand, Nikon D3S has a
12.0MP Full frame (36 x 23.9 mm ) sized CMOS sensor and features Expeed processor.
Leica Q3 Monochrom's sensor provides 48MP more than Nikon D3S's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another difference between these two cameras is that Leica Q3 Monochrom's sensor lacks 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 Q3 Monochrom and D3S sensor size comparison.
Sensor Size and Resolution Comparison image of Leica Q3 Monochrom and Nikon D3S Cameras
Leica Q3 Monochrom and Nikon D3S 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
Leica Q3 Monochrom
or the
Nikon D3S ,
including hyperfocal distance.