Nikon D40X has a
10.0MP APS-C (23.7 x 15.6 mm ) sized CCD sensor and features Expeed processor. On the other hand, Pentax K100D S has a
6.0MP APS-C (23.5 x 15.7 mm ) sized CCD sensor .
Below you can see the D40X and K100D Super sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D40X and Pentax K100D S Cameras
Nikon D40X and Pentax K100D S 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.
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
Nikon D40X
or the
Pentax K100D S ,
including hyperfocal distance.