Nikon D40 has a
6.0MP APS-C (23.7 x 15.5 mm ) sized CCD sensor . On the other hand, Nikon D3100 has a
14.0MP APS-C (23.1 x 15.4 mm ) sized CMOS sensor and features Expeed 2 processor.
Nikon D3100's sensor provides 8MP more than Nikon D40'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 D40 and D3100 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D40 and Nikon D3100 Cameras
Nikon D40 and Nikon D3100 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. Nikon D40 and Nikon D3100 sensors have been tested by DxO and the results show that D3100 has a better overall score of 67, 11 points higher compared to D40's score of 56.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Nikon D40
56
21.0 bits
11.0 Evs
561 ISO
Nikon D3100
67
22.5 bits
11.3 Evs
919 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
Nikon D40
or the
Nikon D3100 ,
including hyperfocal distance.
