Diffraction

Definition

Airy-disk diameter on the sensor is about 2.44 λ N (λ in the same units as the diameter, N the f-number). At 550 nm, f/16 already throws a ~21 µm disk — larger than many pixel pitches and often larger than a 0.030 mm CoC. Stopping down for DoF is real; so is the mush. The “diffraction limit” is a comparison, not a brick wall. Check a test chart at the print size you actually deliver.

Calculators that use this

• Optics & depth of field

  Diffraction Limit Calculator

  Compare the Airy disk at your f-number and wavelength to CoC and pixel pitch to see when stopping down is CoC-limited or pixel-limited.

• Optics & depth of field

  Depth of Field Calculator

  Work out hyperfocal, near and far sharp limits from focal length, f-number, focus distance and circle of confusion. Metres native; toggle feet on location.