Both Nikon D5100 and Panasonic G3 have 16.0 MP resolution sensors but Nikon D5100's sensor is APS-C (23.6 x 15.7 mm ) and Panasonic G3's sensor is Four Thirds (17.3 x 13 mm ).
Since Nikon D5100'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 Panasonic G3.
Below you can see the D5100 and G3 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D5100 and Panasonic G3 Cameras
As seen above, Nikon D5100 has a 1.6x Larger sensor area than Panasonic G3. 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
Both Nikon D5100 and Panasonic G3 sensors have been tested by DxoMark. DxoMark 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. Of the two cameras that we are comparing, D5100 has scored 80, 24 points higher than G3.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Nikon D5100
80
23.5 bits
13.6 Evs
1183 ISO
Panasonic G3
56
21.0 bits
10.6 Evs
667 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
Nikon D5100
or the
Panasonic G3 ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(APS-C versus Four Thirds),
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.
