What is fraunhofer distance?

Fraunhofer distance is a measure of the distance at which the light waves from a source become effectively parallel, ideal for diffraction experiments. It is named after Joseph Fraunhofer, a German optician and physicist. It is also known as Fraunhofer approximation, Fraunhofer limit, or far-field diffraction region.

The Fraunhofer distance is calculated as the distance from the origin of the source of a wavefront at which the wavefront converges to an infinitely distant plane wavefront. It is determined by the size of the aperture or the object being observed and the wavelength of the light used.

In practical terms, this means that if an observer is positioned beyond the Fraunhofer distance from an object or aperture, they will see a diffraction pattern consisting of a series of overlapping bright and dark spots. However, if the observer is positioned closer than the Fraunhofer distance, they will be too close to observe the pattern, and instead, they will see a blurred image.

The Fraunhofer distance is an essential consideration in the design of optical systems, such as telescopes, microscopes, and cameras, as it helps determine the best positioning and sizing of the components to achieve optimal image quality.