Diffraction is when a wave spreads out as it passes through a small slit or any intricate surface. With Photography, this would apply to how the light interacts with the aperture and how the photosites detect it on a sensor.
When light is focused through the aperture, it interacts with the edge of the aperture blades causing it to spread out where its angle bends slightly, this causes a reduction with the maximum optical resolution. The smaller the aperture the greater the effect. You can see a visible real-world example in a harbor or a pond by watching a wave as it bends around a jetty.
Diffraction Calculator
How will diffraction affect your camera?
Use this diffraction calculator to see the limits of diffraction on any given sensor with any number of megapixels.
*This calculator uses pixel pitch (sensor width divided by the number of pixels across) and green light at 0.55 microns. It shows the aperture where the Airy disk grows to about 2.5 times the pixel size, which is roughly where you start to lose fine detail. BSI sensors and better microlenses help each pixel collect more light, but they don’t change the pixel pitch, so the diffraction limit stays the same.
Diffraction | The Equation
The Airy Disc
In optics, we look at diffraction through the Airy Disc or Airy Pattern. A circular pattern named after George Biddell Airy. This doesn’t necessarily reflect what the light is doing in terms of the shape, rather it’s the spread of a power vector. This illustrates that about 84% of the power of the wave is in the first cone and 91% within the first and second cones. That’s why the diameter of that first cone, the Airy disk, is what we use to measure how much detail a lens can resolve at a given aperture. (It’s sometimes confused with the circle of confusion, which is a depth of field concept, not a diffraction one.)
To put it the simplest way possible, as your aperture gets smaller, diffraction causes the Airy Pattern to get larger, and when the diameter is about 2.5x larger than a single pixel on a sensor, there will be a visible reduction in optical resolution.
If you were to shine a laser through an aperture and close that aperture down, you would get a pattern on a wall that looks like this – rendered with Mathematica.
How Aperture Can Ruin A Shot
The smallest spot of detail a lens can produce is 2.44 x Fstop x λ.
Your aperture will have a direct role in the details your lens can produce. For example, if you were to shoot at f19, your smallest spot of perfect detail produced (the Airy Disc diameter) would be (2.44 x 19 x 0.5) = 23.18 microns.
A look at diffraction at various apertures.
Calculations use wavelengths from 0.4 microns (blue) to 0.6 microns (orange), with 0.55 (green) as the average. Deep red light, out near 0.7 microns, spreads a little more. The last column is the bright core of the disk (its width at half brightness), which is only about 0.42 times the full Airy disk diameter.
| F-Stop |
Diffraction Size 0.4-0.6λ (microns) |
Average 0.55 λ |
Bright core (approx.) |
| f19 | 18.54 – 27.82 | 25.5 µm | 7.4 – 11.13 |
| f16 | 15.62 – 23.42 | 21.5 µm | 6.25 – 9.36 |
| f11 | 10.74 – 16.10 | 14.8 µm | 4.3 – 6.44 |
| f8 | 7.81 – 11.71 | 10.7 µm | 3.12 – 4.68 |
| f5.6 | 5.47 – 8.20 | 7.5 µm | 2.19 – 3.28 |
| f4 | 3.90 – 5.87 | 5.4 µm | 1.56 – 2.35 |
| f2.8 | 2.73 – 4.10 | 3.8 µm | 1.09 – 1.64 |
| f2 | 1.95 – 2.93 | 2.7 µm | 0.78 – 1.17 |
It may look like your diffraction spot at f2.8 is 2.73 to 4.10 microns. But the Airy disk doesn’t have hard edges. Most of its energy sits in a bright core only about 0.42 times the full diameter, so in practice there’s more room to play with before you notice diffraction: closer to 1.1 to 1.6 microns at f2.8.
Because the spread depends on wavelength, if you were shooting an image that was primarily blue, you would see less diffraction than if you were to shoot an image that was primarily red.
Diffraction | Real-World Results
How does this relate to our camera sensor and megapixels, and what does diffraction look like in a real-world shoot?
Here is a sample of how diffraction affects the rendering of the Zeiss 35mm f2.8 on the Sony A7r.
How Megapixels Play A Role
When it comes to megapixels, they play a role in overall resolution. The size of the sensor and the number of megapixels determine the size of the pixels on the sensor.
A camera like the Nikon D800 with 36.3 megapixels has a pixel pitch of 4.878. This means that a single pixel is 4.878 microns in size.
If you were to shoot at f19, the smallest spot of perfect detail (the entire airy disc) you could produce is 23.18 microns That’s nearly five pixels wide on the D800, so fine detail gets visibly softer.
To get everything the D800 sensor can resolve, keep the Airy disk under about 2.5 pixels, or roughly 12.2 microns. In green light that works out to about f9. Stop down further and diffraction starts to soften the finest detail. It doesn’t fall off a cliff, but you’re no longer getting the full 36 megapixels’ worth.
This is often why you see some camera manufacturers say that there is a limit to the number of megapixels a camera should have for general use. The more pixels you pack in, the narrower the window of sharp apertures gets: lens aberrations soften the image wide open, and diffraction softens it stopped down. At some point it gets very difficult to actually capture more detail.
Pixel Sizes (In Microns) Based On Megapixels
Sensor sizes have been rounded to produce a close estimate. Canon full-frame is actually 36mm, but the Canon APS-C is actually 22.2mm, whereas the Sony APS-C is 23.6mm. For more on how sensor size affects your images, see our APS-C vs Full Frame guide, and for the practical shooting implications, why you should avoid small apertures.
| Megapixels | Medium Format (53.90mm) | Full Frame (36mm) | APS-C (23.6mm) | Micro 4/3 (17.3mm) | 1/3″ (iPhone) |
| 50MP | 6.60 | 4.16 | 2.73 | 2.12 | — |
| 42MP | 7.20 | 4.53 | 2.97 | 2.31 | — |
| 36MP | 7.78 | 4.90 | 3.21 | 2.50 | — |
| 32MP | 8.24 | 5.20 | 3.41 | 2.65 | — |
| 28MP | 8.82 | 5.55 | 3.64 | 2.83 | — |
| 24MP | 9.53 | 6.00 | 3.93 | 3.06 | — |
| 22MP | 9.95 | 6.26 | 4.11 | 3.19 | 0.87 |
| 18MP | 11.00 | 6.93 | 4.54 | 3.53 | 0.98 |
| 16MP | 11.67 | 7.35 | 4.82 | 3.75 | 1.04 |
| 12MP | 13.47 | 8.49 | 5.56 | 4.33 | 1.2 |
Compare those numbers to the resolution limits at certain apertures and you can see how your lens aperture and diffraction will limit your resolution. At some point, packing more pixels onto a sensor quickly becomes futile.
How Cameras Are Designed Around The Diffraction Limit
Many high-megapixel cameras are designed to resolve perfect details between f5.6 and f8, the sweet spot of most lenses.
While it makes sense for the camera to try to take the megapixel count to the limits of diffraction, some cameras are designed well below the f5.6-f8 limits of diffraction with bigger photosites so they can perform better in low light and with video. Cameras like the Sony A7III and A7sIII for example.
Smartphones are the extreme case. Their pixels are so small that they’re close to the diffraction limit even at their fixed, wide apertures, which is one reason phone cameras don’t stop down.
How Lenses Work With Diffraction
The size of the Airy disk is set by the f-number, so any two lenses at f11 produce the same diffraction. Where lenses differ is how sharp they are before diffraction takes over. A lens with heavy aberrations wide open may still get sharper all the way to f8, while a very sharp lens peaks earlier and then loses detail to diffraction. The one big exception is macro: at close focus the effective aperture is smaller than the marked one, so a 1:1 macro shot at f8 behaves more like f16, and diffraction shows up much sooner.
How Diffraction Can Affect Your Photography
You should be able to see how your aperture and sensor resolution work together. While owning a 50-megapixel camera is great, you’ll have to open up your aperture to fully take advantage of it. This is great for studio and wedding photographers, but not so great for landscape photographers.
When shooting at f8-f16, you likely won’t really see the difference between a 50-megapixel camera or a 42-megapixel camera. Sure, your images will have a larger dimension in size, but the detail should be very close to the same when scaled to match.
Diffraction is even less of a problem if you don’t print to the maximum size of the sensor output.
Why Larger Sensors Are Better
Larger sensors can pack in more megapixels and still come out with a larger pixel pitch. So at the same f-stop, a 50-megapixel medium format camera handles diffraction better than a 50-megapixel full-frame camera, and full frame does better than APS-C. The catch is that a bigger sensor also gives you less depth of field at the same f-stop, so if you stop down further to match the depth of field, most of that advantage disappears.
The Beauty Of More Megapixels
Based on diffraction and sensor microns, you might be thinking that having more megapixels is completely pointless. However, there are some advantages when it comes to image artifacts.
Having a 50-megapixel image and scaling down to 24 megapixels will do a great deal to help eliminate artifacts while still maintaining a very sharp image, compared to a 24-megapixel camera that uses an optical low pass filter to help eliminate artifacts. While optical low pass filters help reduce moire and artifacts, they lower the overall resolution.
In my experience, a 50-megapixel camera with no optical low-pass filter shot at f11 can still hold up against a 24-megapixel camera with a low-pass filter shot at f5.6 once both are scaled to the same size. Simply because the 50-megapixel image is scaling from more pixels, resulting in cleaner diagonal lines, whereas the 24-megapixel camera uses a filter that impacts resolution.
If you removed the optical low-pass filter from the 24-megapixel camera, the detail should be the same, but you would be at a disadvantage regarding moire and aliasing.
What Is Diffraction? | Conclusions
This seems all confusing, but ultimately, what you need to take away is that the more you stop down your aperture, the less detail your lens is capable of producing. This, in turn, can greatly reduce some of the advantages of using a higher-megapixel camera.
While having tons of megapixels packed into your sensor is great, you have to consider the trade-offs. At the same f-stop and megapixel count, APS-C and Micro 4/3 cameras are more affected by diffraction because their pixels are smaller.
Real World Use
Because of diffraction on my Sony A7r III, I typically like to shoot my landscapes at f8 to f11. I know I won’t capture as much detail at f11 as at f8, but that’s ok. F11 is good enough for me and I’m willing to trade more depth of field for slightly less IQ.
The other alternative is to focus on stack. Macro photographers have been doing this for years and if we really want to take advantage of massive megapixel cameras, landscape photographers will have to focus stack. Meaning, shooting at something like f5.6 at various focus ranges and blending the images in post. The other option is medium format, where bigger sensors give you bigger pixels at the same resolution.
I’m not a math genius, but some people who read this will be (although I did finish my College Trig final in 15 minutes). If it looks like I have a mistake, please let me know.
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