Both Sony A9 and Sony A9 II have Full frame sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the A9 and A9 Mark II sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A9 and Sony A9 II Cameras
Sony A9 and Sony A9 II 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. Sony A9 and Sony A9 II sensors have been tested by DxO and the results show that A9 Mark II has a better overall score of 93, 1 points higher compared to A9's score of 92.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A9
92
24.9 bits
13.3 Evs
3517 ISO
Sony A9 II
93
25.0 bits
14.0 Evs
3434 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 A9
or the
Sony A9 II ,
including hyperfocal distance.
