Canon 5D MIII has a
22.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic 5+ processor. On the other hand, Canon 5DS R has a
51.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Dual DIGIC 6 processor.
Canon 5DS R's sensor provides 29MP more than Canon 5D MIII'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 Canon 5DS R'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 5D MIII and 5DS R sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 5D MIII and Canon 5DS R Cameras
Canon 5D MIII and Canon 5DS R 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 5D MIII has 127% larger pixel area compared to Canon 5DS R, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Canon 5D MIII and Canon 5DS R sensors have been tested by DxO and the results show that 5DS R has a better overall score of 86, 5 points higher compared to 5D MIII's score of 81.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Canon 5D MIII
81
24.0 bits
11.7 Evs
2293 ISO
Canon 5DS R
86
24.6 bits
12.4 Evs
2308 ISO
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 5D MIII
or the
Canon 5DS R ,
including hyperfocal distance.
