Photography Calculators

Optics & depth of field

Diffraction Limit Calculator

Every stop down grows the Airy disk. When that blur spot is larger than your CoC, the file is diffraction-limited for that viewing assumption. When it is larger than two pixels, you will see it at 100% even if the print CoC still looks fine. Use this before you set f/16 on a 45 MP body.

Inputs

Units
f/

Taking f-number. Diffraction cares about N, not the lens’s maximum.

nm

550 nm is green, the usual visual default. IR and UV shift the disk.

mm

Same CoC as your DoF calculator so the comparison is fair.

µm

Pitch ≈ sensor width in mm × 1000 / horizontal pixel count.

Results

Airy diameter
14.76µm
Airy diameter
0.0148mm
Diffraction larger than CoC
No
Diffraction larger than 2 pixels
Yes

Recommended gear

Calculation method

Convert wavelength from nanometres to millimetres (divide by one million). The Airy disk diameter is 2.44 times that wavelength times the f-number. The CoC flag is yes when that diameter exceeds the circle of confusion you typed. The pixel flag is yes when the disk is larger than two pixel pitches, a simple stand-in for ‘visible at 100%’.

Exact formula

Airy diameter mm = 2.44 · λ_mm · N, λ_mm = wavelength_nm/1e6. diffractionLimited if Airy > CoC. pixelLimited if Airy > 2 × pixel pitch. Limits: Circular aperture, monochromatic λ; AA filter, demosaic and lens aberrations omitted.

Landscape habit

On full frame, f/8 is often the sweet spot. f/11 is usually fine. f/16 is a DoF choice, not a sharpness choice. Stack or accept the mush if you need more depth.

Wavelength

Blue light diffracts less, red more. 550 nm is the visual compromise. Dedicated astro or IR work should change the wavelength.

Frequently asked questions

Is ‘diffraction limited’ the same as unusable?

No. It means diffraction is no longer smaller than your sharpness budget. Plenty of landscapes at f/11 look fine in print. It is a warning, not a veto.

Why two pixels, not one?

A single photosite is not a resolution limit after demosaic. Two pitches is a common first-order ‘you will see this at 100%’ threshold, not a lab Nyquist test.

Does a better lens beat this?

A sharper lens still diffracts. Glass quality sets the floor at wide apertures; the Airy disk sets it when you stop down. You cannot buy your way out of f/22 on a 45 MP sensor.

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