Olympus E-1 has a
5.0MP Four Thirds (17.3 x 13 mm ) sized CCD sensor . On the other hand, Olympus E-300 has a
8.0MP Four Thirds (17.3 x 13 mm ) sized CCD sensor .
Below you can see the E-1 and E-300 sensor size comparison.
Sensor Size and Resolution Comparison image of Olympus E-1 and Olympus E-300 Cameras
Olympus E-1 and Olympus E-300 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Olympus E-1 has 62% larger pixel area compared to Olympus E-300, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.
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-1
or the
Olympus E-300 ,
including hyperfocal distance.