Ricoh GR III has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor . On the other hand, Ricoh GR IV Monochrome has a
26.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor .
Another similarity between these two cameras is that both Ricoh GR IV Monochrome and Ricoh GR III sensors lack anti-alias (Low-Pass) filters. 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 GR III and GR IV Monochrome sensor size comparison.
Sensor Size and Resolution Comparison image of Ricoh GR III and Ricoh GR IV Monochrome Cameras
Ricoh GR III and Ricoh GR IV Monochrome 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 Ricoh GR III has 6% larger pixel area compared to Ricoh GR IV Monochrome, it has potential to collect more light on pixel level hence 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
Ricoh GR III
or the
Ricoh GR IV Monochrome ,
including hyperfocal distance.