Diffraction Limit

Diffraction is a physical property of light: when light passes through a small opening, it bends and spreads. In photography, as you stop down the aperture, the opening becomes small enough that diffraction begins to soften the image.

Every lens has a diffraction-limited aperture beyond which further stopping down reduces overall sharpness even though depth of field increases. On Fujifilm X-Trans sensors (APS-C, ~23.5mm crop), diffraction becomes visible around f/8-f/11 depending on the sensor resolution.

On the 26MP X-Trans IV/V sensors (X-T4, X-T5, X-H2S), diffraction softening is noticeable from about f/11. On the 40MP X-H2, it starts closer to f/8 because the smaller pixel pitch is more sensitive to diffraction spread.

On GFX medium format (44x33mm sensor), the larger sensor and pixel pitch push the diffraction limit to around f/16-f/22, giving more room to stop down for depth of field.

Practical takeaway: for maximum sharpness on APS-C Fuji cameras, stay between f/5.6 and f/8. Use f/11 only when you need the depth of field. Avoid f/16 and smaller unless depth of field is more important than pixel-level sharpness. For landscapes where you want front-to-back sharpness, focus stacking at f/5.6-f/8 gives better results than shooting at f/16.