We put these two cameras through their paces with noise tests shot at the same time, same lens, same tripod and same subject.
Comparison using our standard daylight test location
100ISO
350D
400D
The 400D image is markedly softer but no real higher noise. I think the softness is some camera shake from wind hitting the tripod and camera, but you can just the noise.
200ISO
350D
400D
400D is slightly softer. Noise is close.
400ISO
350D
400D
400D is still slightly softer. Noise is higher on the 400D.
800ISO
350D
400D
Noise is very comparable.
1600ISO
350D
400D
Noise is higher on the 400D.
Test continues in Part 3 with the uncluttered subject daylight test