Diffraction Limit Calculator

When light passes through a small aperture it spreads slightly, so a point of light is recorded as a tiny blurred disc called the Airy disk rather than a perfect point. The smaller the aperture, meaning the higher the f-number, the larger that disc becomes. Once the Airy disk grows larger than your sensor's pixels can resolve, stopping down further starts to soften fine detail.

Enter the wavelength of light in nanometers in the first field and your aperture as an f-number in the second, for example 8 for f/8. Press Calculate Airy Disk Diameter. The result shows the diameter of the Airy disk in micrometers, calculated with the standard formula of 2.44 multiplied by the wavelength and the f-number.

Visible light runs from roughly 400 nm for violet to about 700 nm for red. Most photographers use 550 nm, green light near the middle of the spectrum, where human vision and most camera sensors are most sensitive. At 550 nm, f/8 gives an Airy disk of about 10.7 micrometers, while f/16 doubles it to about 21.5 micrometers.

Work out your pixel pitch by dividing the sensor width in millimeters by the number of horizontal pixels, then multiplying by 1000 to get micrometers. A 36 mm sensor with 6000 pixels across has a pitch of 6 micrometers. A common rule of thumb is that diffraction softening becomes visible once the Airy disk is more than about two to three pixels wide.

Landscape photographers often stop down for depth of field, but very small apertures trade depth for overall softness. Running the numbers for your own camera shows where that trade-off begins, so you can choose a sweet spot such as f/8 or f/11 and use focus stacking or hyperfocal focusing when you need more depth instead of reaching for f/22.

Yes. The calculator is free, runs instantly in your browser and needs no software or photos. To use the tools, you confirm once that you are a photographer and create or log in to a free Imagen account, and from then on this calculator and every other tool in the collection are open to you on any device.