Image quality is all about the sensor and the electronics. While the Fujifilm GFX100 and the Sony A7R IV differ in electronics, they share the same sensor technology and have exactly the same pixel pitch (pixel size).
In other words, there is a lot to learn about the Sony A7R IV from my reporting on the Fujifilm GFX100.
In terms of sharpness, you lose depth of field (per pixel) and lose micro contrast at the same aperture—a double-whammy since you need to stop down more for the same per pixel depth of field, but doing so degrades the image more!
- Depth of field on a per pixel basis shrinks. The hard requirement for focus stacking for landscape photographers. Which makes it immensely frustrating that the Sony A7R IV appears to lack a focus stepping feature for focus stacking support. Some crappy Sony Play Memories half-assed app won’t do, nor an iPhone app.
- The effects of diffraction on per-pixel micro contrast: on the Sony A7R IV, f/5.6 is subtly affected for high-grade lenses, but f/8 is significantly affected similar to f/10 on the 42MP Sony A7R III. Stopping down is less of a cure than ever before—thing focus stacking when it is feasible.
Other issues might also be similar.
- PDAF banding/striping. Sony had this in the Sony A9 and that was life. The Sony A7R III never gave me trouble, but the Sony A7R IV might. Many cameras (e.g. Nikon Z7) use noise reduction to deal with the striping, generally not a plus for image sharpness.
- Focus accuracy must be 1.2X more accurate to preclude sharpness losses. Fujifilm GFX100 has autofocus issues. I expect Sony to do better however so this point is probably not of concern.
You’ll want things for the Sony A7R IV. Big files mean that a pair of fast SDXC cards for the Sony A7R IV is a must.