Diffraction Calculator
Find the aperture where diffraction starts to limit sharpness for your sensor format.
Results
- Diffraction-limited aperture
- f/22.4
- Airy disk diameter at your aperture
- 10.7 µm
Stopping down beyond this aperture starts to visibly soften detail, even though depth of field keeps increasing. This is the point where softening becomes visible in a standard-sized print. Judged at 100% on a high-resolution sensor, diffraction starts nibbling at per-pixel sharpness several stops earlier.
The size of the smallest point of light your lens can resolve at this aperture, due to diffraction.
How it works
Light bends around the edge of the aperture blades, so a point of light never lands on the sensor as a point. It lands as a small disc surrounded by faint rings, called the Airy disk. The narrower the aperture, the larger that disc grows, and once it outgrows the detail you are trying to record the whole image softens.
This is the trap in stopping down for depth of field. You gain depth right up until diffraction takes more sharpness than the extra depth returns, and past that point the image gets worse everywhere at once.
The figure here is based on the circle of confusion, which asks when softening becomes visible in a standard-sized print. Judged at 100% on a high-resolution sensor the effect appears several stops earlier, so treat this as the point where diffraction becomes obvious rather than the point where it starts.
The formula
Airy disk diameter = 2.44 × λ × N, diffraction limit where that equals c
λ is the wavelength of light, taken as 550nm green, N is the f-number, and c the circle of confusion for the sensor.
Frequently asked questions
- What is my sharpest aperture?
- Usually two to three stops down from wide open, where lens aberrations have faded but diffraction has not yet taken over. For most full-frame lenses that lands between f/5.6 and f/8.
- Do smaller sensors suffer more from diffraction?
- Yes. They need a smaller circle of confusion because the image is enlarged more to reach the same print size, so the same Airy disk does proportionally more damage. Micro Four Thirds hits the limit around a stop and a half earlier than full frame.
- Can sharpening recover diffraction losses?
- Partly. Diffraction is a well-behaved, predictable blur, so deconvolution sharpening recovers some contrast. It cannot restore detail that fell below the noise floor, so it is a rescue rather than a licence to shoot at f/32.
Read more about this
- Hyperfocal focusing in practiceThe technique works. The way it is usually taught puts infinity right on the edge of acceptable, which is the one place you do not want it.
- Why your depth of field calculator disagrees with your photographsThe calculator said the whole scene was sharp. At 100% on screen, half of it clearly is not. Both things are true, and the reason is a number nobody mentions.
- The diffraction limit is not a cliffDiffraction gets talked about as a wall you hit at f/11. It is closer to a slope you have been walking down since f/4.