You wanted everything in a landscape sharp from the foreground rocks to the distant mountains, so you stopped down to f/16 or f/22 — and the result came out softer than the same scene shot at f/8. Nothing was wrong with your focus or your lens. What you're seeing is diffraction, a physical property of light itself. Closing the aperture deepens your depth of field, but past a certain point it also starts eating into the maximum resolving power your lens can deliver.
Why diffraction happens
Light bends slightly as it passes through the small opening formed by the aperture blades, because light behaves as a wave. When the aperture is wide open, this spreading is negligible compared to the size of the image. But as the aperture narrows, the opening itself shrinks, so the spreading becomes proportionally larger. Each point of light on the sensor stops forming a perfect point and instead spreads into a slightly blurred disc (an Airy disk). Once that disk grows large enough to spill across several adjacent pixels, the whole image reads as softer. Diffraction isn't a lens flaw — it's a hard physical limit that no lens design can fully escape.
Sensor pixel pitch decides your diffraction limit, not the lens
The aperture value at which diffraction becomes visible — the diffraction limit — depends far more on your sensor's pixel pitch (pixel size) than on the lens itself. Softening becomes noticeable once the Airy disk's diameter approaches the size of a single pixel. As a rough guide, a high-resolution full-frame body (say, around 45 megapixels, roughly 3.7µm pixel pitch) starts showing diffraction effects around f/8 to f/10, while a lower-resolution 20-megapixel crop-sensor body, with its larger pixel pitch, can often stay sharp up to f/11 or f/13. Very high-resolution medium format or mirrorless bodies can start softening noticeably past just f/8. Before you reach for a smaller aperture for more depth of field, it's worth knowing roughly where your own camera's diffraction limit sits.
A real scenario: choosing f/11 over f/16 for a landscape
Shooting a landscape with a 24mm wide-angle lens, wanting everything sharp from a rock 3 meters away to the horizon, it's tempting to assume "smaller aperture always means more sharpness" and jump straight to f/16 or f/22. But at 24mm, f/11 is often already enough to keep everything from roughly 3 meters to infinity within the depth of field — so there's frequently no need to push into the range where diffraction really bites. Calculating the hyperfocal distance and setting focus there lets you get full depth of field at f/8–f/11 while minimizing diffraction loss. On the other hand, for something like macro work where depth of field is inherently razor-thin and f/16 or f/22 is unavoidable, it's often better to accept the diffraction trade-off through focus stacking — combining multiple shots — rather than relying on an aperture that will inevitably soften detail.
The common mistake: "smaller aperture is always safer"
Especially among landscape beginners, there's a habit of always defaulting to f/16 or narrower on the assumption that more depth of field is unconditionally better. Doing this routinely skips right past the aperture range where most lenses are actually sharpest — typically two to three stops down from wide open, often around f/5.6 to f/8 — and lands you in a softer zone overall. The better approach is to work out how much depth of field the scene actually needs first, then pick the widest aperture within that range that still covers it. If your required depth of field is already satisfied at f/8, there's no reason to stop down further.
Telling diffraction apart from other softness
It also helps to distinguish diffraction softness from other causes of a blurry shot. Camera shake tends to produce directional smearing across the whole frame, while diffraction softens detail evenly and without direction. Missing focus leaves one area sharp and the rest soft, while diffraction reduces fine detail uniformly across the frame, including in the area that's technically in focus. If you're on a tripod, using a timer or remote release to rule out shake, and the image still gets softer the further you stop down, that's diffraction at work.
Checklist
- Learn roughly where your camera's diffraction limit sits based on its pixel pitch — around f/8–f/10 for high-resolution full-frame, f/11–f/13 for typical crop-sensor bodies.
- For landscapes, calculate the depth of field you actually need before stopping down, then pick the widest aperture that still covers it.
- For extreme close-up work with very shallow depth of field, consider focus stacking instead of pushing the aperture further.
- If a shot looks uniformly soft rather than shake-blurred or out of focus, suspect diffraction first.
- Using the hyperfocal distance lets you hold full depth of field at a wider, sharper aperture.