Glossary

Diffraction: divergent nature of a wave due to its limited size
Aperture : diaphragm limiting the number of light rays that are able to propagate
Effective focal length: algebraic distance from the primary/secondary principal plane of an optical system to its front/back focal plane
Lens: optical component with two refractive surfaces axially symmetrical for redirecting the light in a controlled manner
Wavelength ( of a light wave ): distance between two consecutive identical states of the electric ( or magnetic ) field
Back focal plane: plane conjugate by an optical system of an object plane perpendicular to the optical axis and located at infinity
Airy pattern: pattern representing the intensity distribution of a plane monochromatic light wave diffracted by a circular aperture