Both Sony A900 and Sony A850 have Full frame sized 25.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the A900 and A850 sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A900 and Sony A850 Cameras
Sony A900 and Sony A850 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
At Camera Decision, we also look at Dxo Mark sensors when available as we think it is a good indicator of image quality.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A900
79
23.7 bits
12.3 Evs
1431 ISO
Sony A850
79
23.8 bits
12.2 Evs
1415 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
Sony A900
or the
Sony A850 ,
including hyperfocal distance.
