Pentax K-S1 has a
20.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Prime MII processor. On the other hand, Sony A77 has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Bionz processor.
Another difference between these two cameras is that Pentax K-S1's sensor lacks 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 K-S1 and A77 sensor size comparison.
Sensor Size and Resolution Comparison image of Pentax K-S1 and Sony A77 Cameras
Pentax K-S1 and Sony A77 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. On the other hand, since Pentax K-S1 has 20% larger pixel area compared to Sony A77, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.
DxOMark Sensor Scores
At Camera Decision, we also look at Dxo Mark sensors when available as we think it is a good indicator of image quality.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Pentax K-S1
78
23.5 bits
13.0 Evs
1061 ISO
Sony A77
78
24.0 bits
13.2 Evs
801 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
Pentax K-S1
or the
Sony A77 ,
including hyperfocal distance.
