Sony A9 has a
24.0MP Full frame (35.6 x 23.8 mm ) sized Stacked BSI-CMOS sensor and features BIONZ X processor. On the other hand, Panasonic S1R II has a
44.3MP Full frame (36 x 24 mm ) sized CMOS sensor and features Venus Engine processor.
Panasonic S1R II's sensor provides 20.3MP more than Sony A9'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.
One other difference between these two cameras that is worth mentioning is that Panasonic S1R II'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 A9 and S1R II sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A9 and Panasonic S1R II Cameras
Sony A9 and Panasonic S1R II 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
Sony A9
or the
Panasonic S1R II ,
including hyperfocal distance.
