Fujifilm S2 Pro has a
6.0MP APS-C (23 x 15.5 mm ) sized CCD sensor . On the other hand, Pentax K10D has a
10.0MP APS-C (23.5 x 15.7 mm ) sized CCD sensor .
Below you can see the S2 Pro and K10D sensor size comparison.
Fujifilm S2 Pro and Pentax K10D have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.