Diffraction & optimal aperture
Stopping down adds depth of field but eventually diffraction softens the whole frame. See the Airy disc at your aperture and the point where it starts to matter for your format.
Airy disc diameter = 2.44 × λ × f-number (λ ≈ 0.00055mm). Diffraction starts to visibly soften once the Airy disc grows past the format's circle of confusion. Larger formats tolerate smaller apertures.
About this tool
Stopping down deepens focus but eventually diffraction softens the whole frame. This tool shows the Airy disc at your chosen aperture and the point where it grows past your format's circle of confusion, so you know the sharpest working aperture.
How to use it
- Enter the aperture you plan to use.
- Choose your film format to set the circle of confusion.
- Read the Airy disc size and the diffraction-limited aperture.
- Keep at or below that aperture for the crispest results.
FAQ
What is the diffraction-limited aperture?
It is the f-number where the Airy disc equals your format's circle of confusion; stopping down further starts to visibly soften detail.
Why do larger formats allow smaller apertures?
They enlarge less to reach a given print size, so they tolerate a larger Airy disc before softness shows.