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What Is Diffraction?
Janine van der Kooij - Vink
What is diffraction?
Diffraction is the phenomenon in which light bends as it passes along a sharp edge or through a narrow opening, such as your lens aperture. This bending causes the light to behave slightly differently than you might expect, which can affect the sharpness of your image.
To understand what’s happening, it helps to look at the basic principles of light. Light doesn’t behave only as straight rays but also as waves. And waves have the tendency to bend, especially when they pass through a small opening. Think of water waves moving between poles and spreading out on the other side. The same thing happens with light waves that have to pass through a small aperture: they bend, and this deviation causes tiny scatterings or interferences that appear as a slight loss of sharpness.
When does diffraction occur?
In photography, diffraction becomes noticeable when you use a small aperture, for example f/16 or higher. Although such a small aperture increases depth of field, it doesn’t necessarily improve resolution. In fact, the light waves that have to pass through that tiny opening bend and overlap in patterns. This is called a diffraction pattern. The result is that fine details in your photo can appear slightly less sharp, especially when you’re using high-resolution cameras where every detail counts.
A helpful way to visualise diffraction is to imagine a beam of light passing through a narrow slit, creating a pattern of light and dark rings. This corresponds to the characteristic “softness” that can appear at smaller apertures. It’s a natural phenomenon you can’t fully avoid, but you can control it—by choosing slightly larger apertures such as f/8 or f/11, where you often find a good balance between depth of field and image quality.
By understanding diffraction, you can make more intentional aperture choices. This helps you get the most out of your equipment, whether you’re photographing in the Netherlands, Flanders or anywhere in between.
What is the impact of diffraction on image quality?
Although a smaller aperture initially seems to give you more depth of field, it can also lead to visibly softer images. This is known as “image softening”: sharpness and fine details become less defined.
Diffraction primarily affects the resolution of your photo. Even with a high-megapixel camera, too much diffraction can cause details to disappear, as if your image isn’t perfectly in focus. This isn’t due to focusing errors or poor lens quality—it’s simply a physical limitation of light. Landscape photographers or anyone who frequently uses small apertures will notice this effect the most.
A clear example? Photograph a subject at both f/5.6 and f/22 and compare the images at 100%. At f/5.6 you’ll often see extremely sharp fine details. At f/22 those same details appear softer, as though a slight haze lies over the image. The sharpness across the frame may be more consistent, but the resolution still suffers.
In short: every aperture has its own character. If you want maximum sharpness and detail retention, the ideal aperture usually lies between f/5.6 and f/11, depending on your lens. That’s the “sweet spot” where you have minimal diffraction and sufficient depth of field.
How do you recognise and measure diffraction?
How do you see whether diffraction is the issue and not something else, like motion blur or lower lens quality? There are several clear signs and practical ways to identify and even measure diffraction.
Recognising and understanding diffraction allows you to make more informed choices while shooting. This helps you get the best out of your lens and know when to “stop down” your aperture—and when not to.
1. Visual symptoms
One of the clearest signs of diffraction is a general reduction in sharpness, even when your camera is focused perfectly. Especially when shooting with a small aperture, such as f/16 or f/22, you’ll notice that fine details—like grass, hair or stone textures—look less crisp. Everything appears just a little softer, as if a faint veil lies over your image. This is particularly visible in landscape or macro photography, where small apertures are often used for maximum depth of field.
2. Practical tips to identify diffraction
If you want to be sure that diffraction is affecting sharpness, a simple outdoor or studio test can already be revealing. Mount your camera on a tripod and photograph exactly the same subject using different apertures, from wide open (e.g. f/2.8) to very closed (e.g. f/22). Compare the images at 100% in your editing software. If you see sharpness decreasing from a certain aperture onwards, while focus distance and other settings remain identical, then diffraction is most likely the cause.
3. Equipment for measurements
For those who want an even more precise approach, various tools are available. Think of sharpness-analysis software that allows you to measure image sharpness objectively. Professional photographers also use MTF tests (Modulation Transfer Function), which examine how well a lens can reproduce fine details at different apertures. Although quite technical, such analyses can provide valuable insights when you want to maximise the performance of your equipment.
How do you prevent diffraction?
Diffraction is something every photographer encounters sooner or later. It occurs when light rays bend along the edges of a small aperture, causing your photos to lose sharpness. This can happen unnoticed, especially in landscape photography, where small openings (such as f/16 or f/22) are commonly used for greater depth of field. Fortunately, you can minimise it. It all starts with choosing your aperture carefully and understanding your camera system.
The ideal aperture value varies by camera type. On full-frame cameras, the so-called “sweet spot”—the point where your lens performs at its sharpest—typically lies between f/8 and f/11. This way, you retain plenty of sharpness without diffraction becoming an issue. With APS-C cameras, the best results usually occur between f/5.6 and f/8. For micro four thirds systems, which have smaller sensors, the optimal range is around f/4 to f/5.6. Go beyond that, and diffraction may become visible sooner.
Tips for taking sharp photos
Want more depth of field without diffraction? Then you can get creative with other techniques. Try focus stacking, for example, where you combine multiple images with different focus points into one sharp final photo. A sturdy tripod and a remote release also help prevent motion blur, so you don’t have to stop down your aperture too far for extra sharpness.
Experiment with your system to find the perfect balance between sharpness and depth. Take the time to make conscious aperture choices. You’ll see the difference in every detail of your photos.
