Nikon D3000 has a
10.0MP APS-C (23.6 x 15.8 mm ) sized CCD sensor and features Expeed processor. On the other hand, Pentax K-3 III Mono has a
26.0MP APS-C (23 x 15.5 mm ) sized BSI-CMOS sensor and features PRIME V processor.
Pentax K-3 III Mono's sensor provides 16MP more than Nikon D3000'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.
One other difference between these two cameras that is worth mentioning is that Pentax K-3 III Mono's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the D3000 and K-3 III Monochrome sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D3000 and Pentax K-3 III Mono Cameras
Nikon D3000 and Pentax K-3 III Mono 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 D3000
or the
Pentax K-3 III Mono ,
including hyperfocal distance.
