Both Pentax MX-1 and Nikon D3 have 12.0 MP resolution sensors but Pentax MX-1's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Nikon D3's sensor is Full frame (36 x 23.9 mm ).
Since Nikon D3's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Pentax MX-1.
Below you can see the MX-1 and D3 sensor size comparison.
Sensor Size and Resolution Comparison image of Pentax MX-1 and Nikon D3 Cameras
As seen above, Nikon D3 has a 20.7x Larger sensor area than Pentax MX-1. 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 MX-1 and Nikon D3 sensors have been tested by DxO and the results show that D3 has a better overall score of 81, 32 points higher compared to MX-1's score of 49.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Pentax MX-1
49
20.4 bits
11.3 Evs
208 ISO
Nikon D3
81
23.5 bits
12.2 Evs
2290 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 MX-1
or the
Nikon D3 ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(1/1.7-inch 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.
