Diffraction Limit Calculator

Frequently Asked Questions

What is the diffraction limit?

At small apertures light bends around the blades, blurring detail. The Airy disk diameter ≈ 2.44 × λ × f-number; when it exceeds ~2 pixels the lens is diffraction-limited.

What is the DLA?

The Diffraction-Limited Aperture - the f-stop where diffraction softening becomes visible at the pixel level. Higher-resolution sensors (smaller pixels) reach it at wider apertures.

Should I avoid stopping down past it?

Not absolutely - depth of field may matter more than peak sharpness. But beyond ~f/11–f/16 on most cameras, more DOF costs overall resolution.

Does diffraction depend on sensor size?

It depends on pixel pitch, not sensor size directly. Two sensors at the same megapixels but different sizes hit the limit at different f-numbers.

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How This Calculator Works

When light passes through a lens aperture it bends - diffraction - spreading a point of light into an Airy disk whose diameter is Ø = 2.44 × λ × N, where λ is the light wavelength (550 nm green is the default) and N is the f−number. As you stop down, N rises and the Airy disk grows. Once that disk is larger than about two pixels it begins to blur fine detail across photosites no matter how sharp the lens. The pixel pitch comes from the sensor: pitch ≈ sensor width ÷ horizontal pixel count, derived from the megapixel and physical size you select.

Worked Example

A 45 MP full−frame sensor (36 mm wide) has about 8200 pixels across, giving a pitch near 4.4 µm. At f/8 the Airy disk is 2.44 × 0.55 × 8 ≈ 10.7 µm - already wider than 2 × 4.4 = 8.8 µm, so f/8 is mildly diffraction−limited on that body. Solving Ø = 2 × pitch for N gives the diffraction−limited aperture (DLA) ≈ f/6.6: beyond it, total resolution starts dropping. A 24 MP sensor with ~6 µm pixels pushes the DLA out past f/9.

Real-World Use

Landscape and macro shooters use this to choose the sharpest working aperture. The DLA tells you where stopping down further trades depth of field for overall softness - it is the practical sharpness ceiling for that camera. High−resolution bodies (45–61 MP) reach their DLA earlier, which is why f/11 looks crisp on a 24 MP camera but visibly soft on a 61 MP one. For deep focus you may still stop down past the DLA and accept the trade, or use focus stacking instead to keep both depth and acuity.

Common Mistakes

Treating the DLA as a hard wall. Diffraction softening is gradual; one stop past the DLA is usually still usable, two stops is where it gets obvious.

Ignoring wavelength. Blue light (~450 nm) diffracts less than red (~650 nm); the 550 nm default is a luminance−weighted average.

Confusing 'more megapixels = always softer'. A denser sensor hits diffraction earlier per−pixel but still resolves at least as much total detail as a coarser one at the same aperture.

Forgetting effective aperture in macro. At high magnification the effective f−number is larger than the marked one, so diffraction bites sooner.

Limitations & Related Tools

This is a first−order optical model: it ignores the anti−aliasing filter, Bayer demosaic, lens aberrations that may already dominate wide open, and sharpening in post that can partly recover diffraction blur. The "2 pixels" criterion is a common rule of thumb; some workflows use 1 or 3 pixels, shifting the DLA accordingly. Use it as a planning guide, then confirm with a real test chart for your specific lens. Pair it with a depth−of−field calculator to find the aperture that balances focus range against this diffraction limit, and a crop−factor tool when comparing systems.

Diffraction Limit Calculator

Frequently Asked Questions

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