Sony A77 has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Bionz processor. On the other hand, Pentax K-5 IIs has a
16.0MP APS-C (23.7 x 15.7 mm ) sized CMOS sensor and features Prime II processor.
Sony A77's sensor provides 8MP more than Pentax K-5 IIs's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
One other difference between these two cameras that is worth mentioning is that Pentax K-5 IIs'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 and K-5 IIs sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A77 and Pentax K-5 IIs Cameras
Sony A77 and Pentax K-5 IIs have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the 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 A77 and Pentax K-5 IIs sensors have been tested by DxO and the results show that K-5 IIs has a better overall score of 82, 4 points higher compared to A77's score of 78.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A77
78
24.0 bits
13.2 Evs
801 ISO
Pentax K-5 IIs
82
23.9 bits
14.1 Evs
1208 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
or the
Pentax K-5 IIs ,
including hyperfocal distance.
