Both Sony A57 and Sony A55 have APS-C sized 16.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the A57 and A55 sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A57 and Sony A55 Cameras
Sony A57 and Sony A55 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 Sony A57 and Sony A55 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, A57 has scored 75, 2 points higher than A55.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A57
75
23.4 bits
13.0 Evs
785 ISO
Sony A55
73
23.0 bits
12.4 Evs
816 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 A57
or the
Sony A55 ,
including hyperfocal distance.
