Fujifilm X-T4 has a
26.0MP APS-C (23.5 x 15.6 mm ) sized X-Trans CMOS 4 sensor . On the other hand, Sony A6400 has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Bionz X processor.
Another difference between these two cameras is that Fujifilm X-T4'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 X-T4 and A6400 sensor size comparison.
Sensor Size and Resolution Comparison image of Fujifilm X-T4 and Sony A6400 Cameras
Fujifilm X-T4 and Sony A6400 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Sony A6400 has 8% larger pixel area (15.28µm 2 vs 14.12µm 2 ) compared to Fujifilm X-T4, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.
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
Fujifilm X-T4
or the
Sony A6400 ,
including hyperfocal distance.