Both Nikon S30 and Pentax K-m have 10.0 MP resolution sensors but Nikon S30's sensor is 1/3-inch (4.8 x 3.6 mm ) and Pentax K-m's sensor is APS-C (23.5 x 15.7 mm ).
Since Pentax K-m's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon S30.
Below you can see the S30 and K-m sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon S30 and Pentax K-m Cameras
As seen above, Pentax K-m has a 21.4x Larger sensor area than Nikon S30. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in 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 S30
or the
Pentax K-m ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(1/3-inch versus APS-C),
so compare them at the same framing rather than the same focal length.
Put the same focal length on the smaller sensor and it will show less depth of
field, not more, because it also crops tighter. The calculator shows the
full frame equivalent focal length for each body so you can match the framing.
