Glossary

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
Aperture : diaphragm limiting the number of light rays that are able to propagate
Image spot: spot described by the intersection of the observation plane with light rays coming from an object point and transmitted through an optical system
Front focal point: point on the optical axis whose image by an optical system is located at infinity
Depth of field: considering a focus plane conjugate of an object plane by an optical system, defines the maximum shift of the object plane enabling a sharp enough image in the fixed focus plane