Canon 40D has a
10.0MP APS-C (22.2 x 14.8 mm ) sized CMOS sensor . On the other hand, Canon 70D has a
20.0MP APS-C (22.5 x 15 mm ) sized CMOS sensor and features Digic 5+ processor.
Canon 70D's sensor provides 10MP more than Canon 40D'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 40D and 70D sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 40D and Canon 70D Cameras
Canon 40D and Canon 70D 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 40D and Canon 70D sensors have been tested by DxO and the results show that 70D has a better overall score of 68, 4 points higher compared to 40D's score of 64.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Canon 40D
64
22.1 bits
11.3 Evs
703 ISO
Canon 70D
68
22.5 bits
11.6 Evs
926 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 40D
or the
Canon 70D ,
including hyperfocal distance.
