Pentax 645D has a
40.0MP Medium format (44 x 33 mm ) sized CCD sensor and features Prime II processor. On the other hand, Nikon D3X has a
25.0MP Full frame (35.9 x 24 mm ) sized CMOS sensor and features Expeed processor.
Pentax 645D's sensor provides 15MP more than Nikon D3X'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.
Another difference between these two cameras is that Pentax 645D'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 645D and D3X sensor size comparison.
As seen above, Pentax 645D has a 1.7x Larger sensor area than Nikon D3X. 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. Pentax 645D and Nikon D3X sensors have been tested by DxO and the results show that D3X has a better overall score of 88, 6 points higher compared to 645D's score of 82.
Model |
Overall |
Color Depth |
Dynamic Range |
Low-light ISO |
Pentax 645D |
82 |
24.6 bits |
12.6 Evs |
1262 ISO |
Nikon D3X |
88 |
24.7 bits |
13.7 Evs |
1992 ISO |