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glossary

Rigorous stigmatism: Property of certain optical systems for certain characteristic points of the object space such that all the rays coming from one of these points of the object space rigorously pass through a point of the image space (conjugate point) after transmission by the system optical
Refraction index: for a transparent medium, ratio between the light speed in the air and the light speed in the medium ; for a reflective surface in the air or vacuum, the refraction index is « - 1 »
Refracting surface: surface interfacing two transparent media with different refraction indexes
Apex: top of a surface
Weierstrass points: for an elliptic mirror or a spherical refracting surface, points of the optical axis which are rigorous conjugates of each other; for an elliptical mirror, the Weierstrass points are the foci of the ellipse