Diffraction Limit
The aperture beyond which diffraction, rather than lens design or sensor resolution, becomes the factor limiting sharpness.
Formula / rule
N_limit ≈ pixel pitch / 1.22λ
Measured in
f-stops
In depth
The limit depends on pixel pitch, not sensor size, so a high-resolution body reaches it at a wider aperture than a lower-resolution one of the same format. Passing it does not ruin an image — the loss is gradual and often worth trading for depth of field — but it does mean extra megapixels stop buying detail.
Examples in practice
A 61-megapixel full-frame body is diffraction-limited from about f/5.6, while a 24-megapixel body holds out to about f/9.