Both Sony A77 II and Pentax K-3 II have APS-C sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
One other difference between these two cameras that is worth mentioning is that Pentax K-3 II's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the A77 II and K-3 II sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A77 II and Pentax K-3 II Cameras
Sony A77 II and Pentax K-3 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
Both Sony A77 II and Pentax K-3 II 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, A77 II has scored 82, 2 points higher than K-3 II.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A77 II
82
24.4 bits
13.4 Evs
1013 ISO
Pentax K-3 II
80
23.6 bits
13.6 Evs
1106 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 A77 II
or the
Pentax K-3 II ,
including hyperfocal distance.
