Pentax K-3 has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Prime III 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.
Another difference between these two cameras is that Pentax K-3'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-3 and D3X sensor size comparison.
Sensor Size and Resolution Comparison image of Pentax K-3 and Nikon D3X Cameras
As seen above, Nikon D3X has a 2.4x Larger sensor area than Pentax K-3. 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 K-3 and Nikon D3X sensors have been tested by DxO and the results show that D3X has a better overall score of 88, 8 points higher compared to K-3's score of 80.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Pentax K-3
80
23.7 bits
13.4 Evs
1216 ISO
Nikon D3X
88
24.7 bits
13.7 Evs
1992 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-3
or the
Nikon D3X ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(APS-C versus Full frame),
so compare them at the same framing rather than the same focal length.
Put the same focal length on the smaller sensor and it will show less depth of
field, not more, because it also crops tighter. The calculator shows the
full frame equivalent focal length for each body so you can match the framing.
