Nikon D3100 has a
14.0MP APS-C (23.1 x 15.4 mm ) sized CMOS sensor and features Expeed 2 processor. On the other hand, Pentax K100D S has a
6.0MP APS-C (23.5 x 15.7 mm ) sized CCD sensor .
Nikon D3100's sensor provides 8MP more than Pentax K100D S's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the D3100 and K100D Super sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D3100 and Pentax K100D S Cameras
Nikon D3100 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 D3100
or the
Pentax K100D S ,
including hyperfocal distance.
