About this calculator
Every lens is sharpest wide open in terms of diffraction, and gets softer past a certain aperture as the diffraction pattern (the "Airy disk") grows larger than the circle of confusion your sensor size can resolve. This calculator finds that diffraction-limited aperture for your sensor, using the standard Rayleigh-criterion approximation (Airy disk diameter ≈ 2.44 × wavelength × f-number, with a 550nm reference wavelength), and shows the classic hyperfocal-based depth of field for your chosen aperture and subject distance side by side — so you can weigh "more depth of field" against "more diffraction softening" for the same shot.
How the calculation works
The Airy disk diameter is about 2.44 × wavelength × f-number, using a reference wavelength of 550 nm, the middle of visible light. The f-number at which that diameter equals the circle of confusion set by your sensor size is the diffraction-limited aperture: circle of confusion ÷ (2.44 × wavelength).
Depth of field uses the same hyperfocal formulas as the DoF calculator, so the diffraction limit and depth of field appear side by side for the same aperture. You can weigh the sharpness you lose to diffraction against the depth of field you gain by stopping down.
Worked examples
- The diffraction-limited apertures by sensor are about f/22.4 for full frame, f/26.8 for medium format, f/14.9 for APS-C, f/11.2 for Micro Four Thirds and f/8.2 for 1-inch. The smaller the sensor, the sooner diffraction shows.
- At f/16 the Airy disk is about 0.0215 mm (21.5 μm). That is smaller than the full-frame circle of confusion of 0.03 mm, so it is within the limit, but on APS-C (0.02 mm) it is about 7% past the limit and on Micro Four Thirds (0.015 mm) about 43% past.
- On full frame with a 24 mm lens focused at 3 m, the near limit is about 1.35 m at f/8, about 0.87 m at f/16 and about 0.69 m at f/22. Beyond f/8, each extra stop buys less and less depth of field.
- On APS-C with a 35 mm lens focused at 2 m, the sharp zone at f/8 is about 1.59 to 2.69 m, widening to about 1.33 to 4.07 m at f/16. But f/16 is past this sensor's diffraction limit of about f/14.9.
When to use it
It is most useful in landscape and architecture work when deciding how far you can stop down for depth of field. If you plan large prints or heavy crops, you can check in advance how much an aperture past the diffraction limit will cost you.
Limits and common mistakes
- Passing the diffraction limit does not make a photo unusable. Softness grows gradually, and when depth of field matters more, an aperture past the limit can be the better choice.
- The calculation is an approximation using a fixed wavelength and a standard circle of confusion, so real lens resolution and sensor megapixels will change the outcome.
- A lens's sharpest aperture is usually two or three stops down from wide open, which is a separate factor from the diffraction limit.
- Results assume screen-size viewing. At 100% zoom, diffraction can show at an earlier aperture.
- A custom circle of confusion must be between 0.001 and 0.1 mm. Use it only when you know the right value for your sensor.
Guides that pair well with this calculator
An approximation using a fixed reference wavelength and standard circle-of-confusion values — real-world sharpness also depends on your specific lens, sensor resolution, and how the image is viewed or printed.
Frequently Asked Questions
What does "diffraction-limited aperture" mean?+
It's the narrowest aperture (smallest f-number) past which diffraction becomes the main thing softening fine detail in a photo, for a given sensor size. Stopping down further still deepens depth of field, but at the cost of increasingly visible softening.
Why is the diffraction-limited aperture different for each sensor size?+
It depends on the circle of confusion, which is based on sensor size (via the same values our DoF calculator uses) — a smaller sensor has a smaller circle of confusion, so diffraction becomes visible at a wider aperture (a lower f-number) than on a larger sensor.
Should I avoid diffraction-limited apertures entirely?+
Not necessarily — depth of field is often more important to the final image than the small amount of softening near the diffraction limit. It matters most when you need maximum resolved detail, such as large prints or heavy crops.