Both Nikon D90 and Nikon D300S 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 D90 and D300S sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D90 and Nikon D300S Cameras
Nikon D90 and Nikon D300S have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.
DxOMark Sensor Scores
Both Nikon D90 and Nikon D300S 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, 3 points higher than D300S.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Nikon D90
73
22.7 bits
12.5 Evs
977 ISO
Nikon D300S
70
22.5 bits
12.2 Evs
787 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
Nikon D300S ,
including hyperfocal distance.
