Both Nikon D3000 and Canon 400D have APS-C sized 10.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the D3000 and 400D sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D3000 and Canon 400D Cameras
As seen above, Nikon D3000 has a 1.1x Larger sensor area than Canon 400D. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
At Camera Decision, we also look at Dxo Mark sensors when available as we think it is a good indicator of image quality.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Nikon D3000
62
22.3 bits
11.1 Evs
563 ISO
Canon 400D
62
22.1 bits
11.0 Evs
664 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 D3000
or the
Canon 400D ,
including hyperfocal distance.
