Both Fujifilm S3 Pro and Fujifilm S5 Pro have APS-C sized 6.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the S3 Pro and S5 Pro sensor size comparison.
Sensor Size and Resolution Comparison image of Fujifilm S3 Pro and Fujifilm S5 Pro Cameras
Fujifilm S3 Pro and Fujifilm S5 Pro 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
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. Fujifilm S3 Pro and Fujifilm S5 Pro sensors have been tested by DxO and the results show that S5 Pro has a better overall score of 65, 5 points higher compared to S3 Pro's score of 60.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Fujifilm S3 Pro
60
20.9 bits
13.5 Evs
346 ISO
Fujifilm S5 Pro
65
21.6 bits
13.5 Evs
448 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
Fujifilm S3 Pro
or the
Fujifilm S5 Pro ,
including hyperfocal distance.
