Both Sony A7S III and Canon 450D have 12.0 MP resolution sensors but Sony A7S III's sensor is Full frame (35.6 x 23.8 mm ) and Canon 450D's sensor is APS-C (22.2 x 14.8 mm ).
Since Sony A7S III'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 Canon 450D.
Below you can see the A7S III and 450D sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A7S III and Canon 450D Cameras
As seen above, Sony A7S III has a 2.6x Larger sensor area than Canon 450D. 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 Sony A7S III and Canon 450D 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, A7S III has scored 85, 24 points higher than 450D.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A7S III
85
24.2 bits
13.4 Evs
3900 ISO
Canon 450D
61
21.9 bits
10.8 Evs
692 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
Sony A7S III
or the
Canon 450D ,
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.
