Both Nikon D90 and Olympus E-620 have 12.0 MP resolution sensors but Nikon D90's sensor is APS-C (23.6 x 15.8 mm ) and Olympus E-620's sensor is Four Thirds (17.3 x 13 mm ).
Since Nikon D90's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus E-620.
Below you can see the D90 and E-620 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D90 and Olympus E-620 Cameras
As seen above, Nikon D90 has a 1.7x Larger sensor area than Olympus E-620. 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
Both Nikon D90 and Olympus E-620 sensors have been tested by DxoMark. DxoMark 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. Of the two cameras that we are comparing, D90 has scored 73, 18 points higher than E-620.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Nikon D90
73
22.7 bits
12.5 Evs
977 ISO
Olympus E-620
55
21.3 bits
10.3 Evs
536 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 D90
or the
Olympus E-620 ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(APS-C versus Four Thirds),
so compare them at the same framing rather than the same focal length.
Put the same focal length on the smaller sensor and it will show less depth of
field, not more, because it also crops tighter. The calculator shows the
full frame equivalent focal length for each body so you can match the framing.
