Both Nikon D750 and Sony A77 have 24.0 MP resolution sensors but Nikon D750's sensor is Full frame (35.9 x 24 mm ) and Sony A77's sensor is APS-C (23.5 x 15.6 mm ).
Since Nikon D750'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 Sony A77.
Below you can see the D750 and A77 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D750 and Sony A77 Cameras
As seen above, Nikon D750 has a 2.4x Larger sensor area than Sony A77. 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 D750 and Sony A77 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, D750 has scored 93, 15 points higher than A77.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Nikon D750
93
24.8 bits
14.5 Evs
2956 ISO
Sony A77
78
24.0 bits
13.2 Evs
801 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 D750
or the
Sony A77 ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(Full frame versus APS-C),
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.
