Blackmagic PYXIS 6K has a
24.0MP Full frame (36 x 24 mm ) sized CMOS sensor . On the other hand, Nikon D800 has a
36.0MP Full frame (35.9 x 24 mm ) sized CMOS sensor and features Expeed 3 processor.
Nikon D800's sensor provides 12MP more than Blackmagic PYXIS 6K'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.
Below you can see the PYXIS 6K and D800 sensor size comparison.
Sensor Size and Resolution Comparison image of Blackmagic PYXIS 6K and Nikon D800 Cameras
Blackmagic PYXIS 6K and Nikon D800 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
Blackmagic PYXIS 6K
or the
Nikon D800 ,
including hyperfocal distance.