Canon C50 has a
32.5MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic DV7 processor. On the other hand, Canon 1D X III has a
20.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic X processor.
Canon C50's sensor provides 12.5MP more than Canon 1D X III'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 C50 and 1D X MIII sensor size comparison.
Sensor Size and Resolution Comparison image of Canon C50 and Canon 1D X III Cameras
Canon C50 and Canon 1D X III have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Canon 1D X III has 71% larger pixel area (43.29µm 2 vs 25.26µm 2 ) compared to Canon C50, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.
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 C50
or the
Canon 1D X III ,
including hyperfocal distance.