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glossary

Object: element (point, line, plane, or whatever,…) of the space linked to another element called image in a way that rays coming from the object and transmitted by an optical system focus on the image ; object and image are said to be conjugate by the optical system
Image: conjugate of an object by an optical system (see object)
Transverse magnification: size ratio of an image and an object, the image being conjugated to the object by an optical system; for centered optical systems, the transverse magnification is defined with objects in a plane perpendicular to the optical axis - transverse magnification is then positive if object and image have the same orientation and negative otherwise
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