Comparing Sony A7R IV to Sony A7R III Resolution: Pine Creek Mining Buildings
A similar study was done with the Sigma 35mm f/1.2 DG DN Art in View Past Greenstone Lake to North Peak.
This meticulous study looks at the real-world 1.2X linear resolving power difference of the Sony A7R IV versus the Sony A7R III on a finely detailed distant scene. Nothing short of perfect shot discipline and the very best lens is likely to match this comparison’s articulation of the differences. Based on the care I took, and other comparisons I’ve done between the A7R III and A7R IV, I consider it definitive as to potential of the A7R IV detail capture.
Extensive discussion. Everything matters, including how the images are upscaled.
Shootout of Sony A7R IV vs Sony A7R III: Pine Creek Mining Buildings
Includes images up to 138 megapixels plus crops from the 138MP images from f/2 through f/8 for both cameras with both Gigapixel AI and Photoshop upscaling. Plus the full resolution as-shot images from both cameras.
I worked hard to get things just right for comparison purposes. It took the right lens, the right subject at the right distance, and the right conditions (e.g, no wind).

Sony A7R IV + Voigtlander FE Macro APO-Lanthar 65mm f/2 Aspherical + polarizer Zeiss
ENV: Pine Creek Tungsten Mine, altitude 8250 ft / 2515 m, 60°F / 15°C
RAW: Enhance Details, LACA corrected, vignetting corrected, +100 Shadows, -100 Highlights, +50 Whites
[low-res image for bot]