Nikon A100 has a
20.0MP 1/2.3' (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Fujifilm X-T1 IR has a
16.0MP APS-C (23.6 x 15.6 mm ) sized CMOS X-TRANS II sensor and features EXR Processor II processor.
One other difference between these two cameras that is worth mentioning is that Fujifilm X-T1 IR'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 A100 and X-T1 IR sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon A100 and Fujifilm X-T1 IR Cameras
As seen above, Fujifilm X-T1 IR has a 13.1x Larger sensor area than Nikon A100. 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 A100
or the
Fujifilm X-T1 IR ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(1/2.3' 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.