Prerequisites

Figure 1: Classical thick model, in an homogeneous fluid

• Conjugate planes: if an optical system makes the rays from an object point $A_o$ converge to a point $A_i$, then $A_i$ is said to be the image or equivalently the conjugate of $A_o$.

• Transversal magnification: ($Gt$). If $x_{Ao}$ and $x_{Ai}$ are the respective distances of points $A_o$ and $A_i$ to the optical axis, the transversal magnification $Gt$ is equal to the ratio of these distances:
  $$Gt=\frac{x_{Ai}}{x_{Ao}}$$

• Angular magnification: ($Ga$). Angular magnification denotes the ratio of the incident and emergent angles $(u_o,u_i)$ of an optical ray going through two conjugate points of the optical axis.
  $$Ga= (\frac{u_{i}}{u_{o}})_{x=0,y=0}$$

• Principal planes and points: object and image principal planes are conjugate planes orthogonal to the optical axis such that the transversal magnification is one. This definition implies that the rays between these two planes are parallel to the optical axis.

  Principal points are the intersection of the principal planes with the optical axis.

• Focal length: $fi$. This is the distance ($H_i F_i$) where $F_i$ is the image focal point. We recall that the image of an object located at infinity undergoes no blurring at the focal point.

• Nodal points: These are the pair of conjugate points on the optical axis $N_o$ et $N_i$ such that every ray through $N_o$ emerges at $N_i$ without change of direction (i.e. the angular magnification is one).