OM System OM-3 has a
20.0MP Four Thirds (17.4 x 13 mm ) sized Stacked BSI Live MOS Sensor sensor and features TruePic X Dual Quad Core processor. On the other hand, Leica M-E Typ 220 has a
18.0MP Full frame (36 x 24 mm ) sized CCD sensor .
Another difference between these two cameras is that OM System OM-3's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the OM-3 and M-E Typ 220 sensor size comparison.
Sensor Size and Resolution Comparison image of OM System OM-3 and Leica M-E Typ 220 Cameras
As seen above, Leica M-E Typ 220 has a 3.8x Larger sensor area than OM System OM-3. 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
OM System OM-3
or the
Leica M-E Typ 220 ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(Four Thirds 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.