Diffraction Limit Calculator

Frequently Asked Questions

Does more megapixels always mean a lower (more restrictive) DLA?

Yes - more pixels means smaller pixels, which means the Airy disk covers two pixels at a wider aperture. However, the denser sensor still resolves at least as much total detail at a given aperture as a coarser one.

Why is the default wavelength 550 nm?

550 nm (green) is the peak sensitivity of the human eye's photopic vision. It gives a conservative but realistic estimate because green is weighted most heavily in luminance calculations.

Is the DLA a hard limit?

No. It is the aperture at which diffraction begins to dominate, but real image quality depends on the anti-aliasing filter, demosaicing, lens aberrations, and post-processing. Use it as a planning guide, then verify with your own test chart.

How does macro photography affect diffraction?

At 1:1 magnification the effective f-number doubles - f/8 on the ring becomes f/16 effective. This means diffraction appears much earlier than the DLA for macro work; factor in the magnification when planning aperture.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How It Works

When light passes through a circular aperture, diffraction causes a point source to spread into an Airy disk rather than a perfect point. The diameter of that disk is: Airy disk diameter = 2.44 x wavelength x f-number. As you stop down (increase the f-number), the Airy disk grows larger. Once the disk covers roughly two pixels, it begins to blur detail across photosites regardless of how sharp the lens is optically.

The diffraction-limited aperture (DLA) is the f-number at which the Airy disk equals two pixel pitches: DLA = (2 x pixel_pitch) / (2.44 x wavelength). For visible light the default wavelength is 550 nm (green, which the human eye weights most heavily for luminance).

Pixel pitch is calculated from the sensor preset: pitch = sensor_width / horizontal_pixel_count, derived from the megapixel count and physical sensor dimensions you select. Higher megapixel counts mean smaller pixels and a lower DLA - high-resolution sensors hit diffraction softening sooner as you stop down.

Use Cases

The diffraction limit matters in any situation where you need maximum overall sharpness:

Landscape photography: finding the ideal aperture range before diffraction noticeably softens the image

Comparing a 24 MP vs. 45 MP or 61 MP body to understand which demands more careful aperture selection

Macro photography: at 1:1 magnification the effective f-number is doubled, so the DLA bites twice as fast

Product and studio work: determining whether f/11 delivers acceptable sharpness on a given camera

Planning focus-stacking sessions when you need deep DOF beyond the DLA

Tips

Diffraction softening is gradual - one stop past the DLA is usually still acceptable, and two stops past is where it becomes obvious at print size.

The DLA shifts with wavelength; blue light (~450 nm) diffracts less than red (~650 nm), so blue-biased subjects hold resolution slightly longer.

At macro magnifications, multiply your nominal f-number by (1 + magnification) to find the effective aperture, then compare to the DLA.

On high-resolution bodies, consider focus stacking with a wider aperture instead of stopping down past the DLA to gain depth of field.

Sharpening in post-processing can partially recover mild diffraction softening, but it cannot equal optical sharpness achieved at or below the DLA.

FAQ