Sony A9 has a
24.0MP Full frame (35.6 x 23.8 mm ) sized Stacked BSI-CMOS sensor and features BIONZ X processor. On the other hand, Pentax 645Z has a
51.0MP Medium format (44 x 33 mm ) sized CMOS sensor and features PRIME III processor.
Pentax 645Z's sensor provides 27MP more than Sony A9'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 645Z'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 A9 and 645Z sensor size comparison.
As seen above, Pentax 645Z has a 1.7x Larger sensor area than Sony A9. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in 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 Pentax 645Z sensors have been tested by DxO and the results show that 645Z has a better overall score of 101, 9 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 |
Pentax 645Z |
101 |
26.0 bits |
14.7 Evs |
4505 ISO |