Pentax 645D has a
40.0MP Medium format (44 x 33 mm ) sized CCD sensor and features Prime II processor. On the other hand, Canon 90D has a
33.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features DIGIC 8 processor.
Pentax 645D's sensor provides 7MP more than Canon 90D'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.
Another difference between these two cameras is that Pentax 645D's sensor lacks 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 645D and 90D sensor size comparison.
Sensor Size and Resolution Comparison image of Pentax 645D and Canon 90D Cameras
As seen above, Pentax 645D has a 4.4x Larger sensor area than Canon 90D. 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
Pentax 645D
or the
Canon 90D ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(Medium format 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.
