Both Canon 70D and Pentax K-S1 have 20.0 MP resolution sensors but Canon 70D's sensor is APS-C (22.5 x 15 mm ) and Pentax K-S1's sensor is APS-C (23.5 x 15.6 mm ).
Since Pentax K-S1's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Canon 70D.
One other difference between these two cameras that is worth mentioning is that Pentax K-S1'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 70D and K-S1 sensor size comparison.
Canon 70D and Pentax K-S1 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.
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 70D and Pentax K-S1 sensors have been tested by DxO and the results show that K-S1 has a better overall score of 78, 10 points higher compared to 70D's score of 68.
Model |
Overall |
Color Depth |
Dynamic Range |
Low-light ISO |
Canon 70D |
68 |
22.5 bits |
11.6 Evs |
926 ISO |
Pentax K-S1 |
78 |
23.5 bits |
13.0 Evs |
1061 ISO |