Canon D30 has a
3.0MP APS-C (22.7 x 15.1 mm ) sized CMOS sensor . On the other hand, Canon 10D has a
6.0MP APS-C (22.7 x 15.1 mm ) sized CMOS sensor .
Below you can see the D30 and 10D sensor size comparison.
Canon D30 and Canon 10D 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 Canon D30 has 102% larger pixel area compared to Canon 10D, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.