Prisms

A prism of index n is composed of two dioptric planes forming an angle A. Following figure 20, a luminous ray enters from side 1 under incidence i and comes out of side 2 under incidence i', the corresponding refraction angles in the prism are r and r', D is the deviation from the ray provoqued by the prism. The angular sign convention is normal for side 1 and inversed for side 2.

We have the following form :

sin(i) = n.sin(r)

sin(i') = n.sin(r')

A = r + r'

D = i + i' - A

At the minimum of deviation : i = i' et r = r', we obtain a relationship between n, A and D, allowing index measures of optical material :