Design Nomenclature / Light & Optics
Diffraction
Also called diffraction limit, aperture diffraction
This entry has not been translated yet and is shown in English.
The spreading and interference of light as it passes an edge or aperture — a wave effect rather than a ray one. It sets the resolution floor of any optical system, puts the star points on a stopped-down aperture, and produces the rainbow sheen on a disc's pitch.
In practice
Why stopping down past roughly f/11 stops buying sharpness and starts costing it: depth of field keeps growing while the diffraction limit closes in faster.
Not to be confused with
- DispersionThe dependence of refractive index on wavelength, so a single refraction sends each wavelength off at a slightly different angle. It is what a prism does, what builds a rainbow, and — inside a lens — what chromatic aberration is: the same image formed at slightly different scales per colour.
- RefractionThe bending of light as it crosses between media of differing index, because its phase velocity changes; Snell's law fixes the new angle from the ratio of the two indices. It is what makes a submerged rod look broken and what gives a lens any power at all.