Both Olympus E-500 and Canon 20D have 8.0 MP resolution sensors but Olympus E-500's sensor is Four Thirds (17.3 x 13 mm ) and Canon 20D's sensor is APS-C (22.5 x 15 mm ).
Since Canon 20D'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 Olympus E-500.
Below you can see the E-500 and 20D sensor size comparison.
Sensor Size and Resolution Comparison image of Olympus E-500 and Canon 20D Cameras
As seen above, Canon 20D has a 1.5x Larger sensor area than Olympus E-500. 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.
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
Olympus E-500
or the
Canon 20D ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(Four Thirds 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.
