Olympus SP-810 UZ has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features TruePic III+ processor. On the other hand, Olympus E-420 has a
10.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features TruePic III processor.
Below you can see the SP-810 UZ and E-420 sensor size comparison.
As seen above, Olympus E-420 has a 8.0x Larger sensor area than Olympus SP-810 UZ. 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.