Both Canon 450D and Nikon D5000 have APS-C sized 12.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the 450D and D5000 sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 450D and Nikon D5000 Cameras
As seen above, Nikon D5000 has a 1.1x Larger sensor area than Canon 450D. 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
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 450D and Nikon D5000 sensors have been tested by DxO and the results show that D5000 has a better overall score of 72, 11 points higher compared to 450D's score of 61.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Canon 450D
61
21.9 bits
10.8 Evs
692 ISO
Nikon D5000
72
22.7 bits
12.5 Evs
868 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 450D
or the
Nikon D5000 ,
including hyperfocal distance.
