Diffraction Limit Calculator
Where diffraction starts to cost you sharpness — f/21.6 or f/4.5 on the same camera, depending entirely on whether you measure against a print or a pixel.
This is diffraction alone. The aperture a lens is actually sharpest at is a balance between diffraction, which worsens as you stop down, and aberrations, which improve — so the sweet spot is usually a stop or two below maximum and no formula here can find it for your lens. What the limit gives you is the ceiling, not the optimum. Nothing is uploaded.
The same camera has two diffraction limits, five times apart
The Airy disc "starts to matter" when it fills whatever blur you are willing to accept — and the two sensible choices are nothing alike. Against a full-frame print's circle of confusion that is f/21.6; against a single pixel on a 24 MP sensor it is f/4.47. The same lens, the same physics, a factor of 4.8 apart. Neither is wrong. They answer different questions, and quoting one as "the" diffraction limit is how the argument about high-resolution bodies looking soft got started: on a 61 MP body the pixel limit is f/2.82, so nearly every aperture is limited at 100% — while the print from it still holds more detail than the 24 MP one at every aperture, because it still has more pixels.
| Measured against | Acceptable blur | Limit |
|---|---|---|
| Full frame print | 0.0290 mm | f/21.61 |
| APS-C print | 0.0190 mm | f/14.16 |
| 24 MP full frame pixel | 0.0060 mm | f/4.47 |
| 45 MP full frame pixel | 0.0044 mm | f/3.27 |
| 61 MP full frame pixel | 0.0038 mm | f/2.82 |
| 20 MP Micro Four Thirds pixel | 0.0033 mm | f/2.49 |
More pixels always means an earlier pixel-level limit, not a later one — a finer grid resolves the blur sooner. And every print limit beats every pixel limit, because a print's tolerance is far larger than a photosite.
What the disc is actually doing
The Airy disc is 2.44·λ·N across, so it grows straight with the f-number — double the f-number and you double the disc. Wide open it spans under half a pixel on a 24 MP full frame, which means the sensor cannot see it at all. It crosses one pixel between f/4 and f/5.6 — exactly where the f/4.47 limit says it should, which is the two tables agreeing by different routes. By f/22 it spans nearly five pixels and has finally filled the print's circle too.
| Aperture | Airy disc | Against the print circle | In pixels (24 MP) |
|---|---|---|---|
| f/1.4 | 0.0019 mm | 0.06× | 0.31 |
| f/2 | 0.0027 mm | 0.09× | 0.45 |
| f/2.8 | 0.0038 mm | 0.13× | 0.63 |
| f/4 | 0.0054 mm | 0.19× | 0.89 |
| f/5.6 | 0.0075 mm | 0.26× | 1.25 |
| f/8 | 0.0107 mm | 0.37× | 1.79 |
| f/11 | 0.0148 mm | 0.51× | 2.46 |
| f/16 | 0.0215 mm | 0.74× | 3.58 |
| f/22 | 0.0295 mm | 1.02× | 4.92 |
Colour changes it too, and less than the sensor does. Blue light diffracts less than red, so the limit runs from f/26.4 in blue to f/18.3 in red — about a third, or half a stop at most, against the fivefold spread between measuring pixels and measuring prints.
| Colour | Wavelength | Print limit |
|---|---|---|
| Blue | 450 nm | f/26.41 |
| Green | 550 nm | f/21.61 |
| Red | 650 nm | f/18.28 |
How to use
- Enter your sensor width and pixel count.
- Enter the aperture you want to check.
- Adjust the print circle of confusion if you like.
- Read both limits and how large the Airy disc is.
Frequently asked questions
What is the diffraction limit?
The f-number at which the Airy disc grows large enough to fill whatever blur you are willing to accept. The disc is 2.44 times the wavelength times the f-number, so it grows straight as you stop down.
Why do I see two different numbers quoted?
Because the answer depends entirely on what you measure against. A full-frame print circle of confusion gives f/21.6; a single pixel on a 24 MP sensor gives f/4.47. Nearly five times apart, and neither is wrong.
Does a higher-resolution sensor diffract sooner?
At the pixel level, yes — a finer grid resolves the blur earlier. A 61 MP full frame is pixel-limited from about f/2.8. That is why such bodies look soft at 100% stopped down.
So is a high-resolution camera worse?
No, and this is the part the argument usually misses. The print from it still holds more detail at every aperture, because it still has more pixels. Softness at 100% and detail in the print are different measurements.
What aperture is my lens sharpest at?
This cannot tell you. Sharpness is a balance between diffraction, which worsens as you stop down, and aberrations, which improve — so the sweet spot is usually a stop or two below maximum. The limit is a ceiling, not an optimum.
Does the colour of the light matter?
A little. Blue diffracts less than red, so the limit runs from about f/26 in blue to f/18 in red — roughly a third, or half a stop. That is far less than the fivefold spread between measuring pixels and measuring prints.
When can the sensor not see diffraction at all?
When the disc is smaller than a photosite. Wide open on a 24 MP full frame it spans under half a pixel, so it costs nothing whatsoever; it crosses one pixel between f/4 and f/5.6.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.