Canon 10D has a
6.0MP APS-C (22.7 x 15.1 mm ) sized CMOS sensor . On the other hand, Canon D30 has a
3.0MP APS-C (22.7 x 15.1 mm ) sized CMOS sensor .
Below you can see the 10D and D30 sensor size comparison.
Canon 10D and Canon D30 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 (110.22µm2 vs 54.49µm2) compared to Canon 10D, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.