Both Nikon D2Xs and Nikon D3S have 12.0 MP resolution sensors but Nikon D2Xs's sensor is APS-C (23.7 x 15.7 mm ) and Nikon D3S's sensor is Full frame (36 x 23.9 mm ).
Since Nikon D3S'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 Nikon D2Xs.
Below you can see the D2Xs and D3S sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D2Xs and Nikon D3S Cameras
As seen above, Nikon D3S has a 2.3x Larger sensor area than Nikon D2Xs. 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. Nikon D2Xs and Nikon D3S sensors have been tested by DxO and the results show that D3S has a better overall score of 82, 23 points higher compared to D2Xs's score of 59.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Nikon D2Xs
59
22.2 bits
10.9 Evs
489 ISO
Nikon D3S
82
23.5 bits
12.0 Evs
3253 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 D2Xs
or the
Nikon D3S ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(APS-C versus Full frame),
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.
