🔺 Prism — how deviation δ depends on the incidence angle i

A ray refracts in, crosses the prism, and refracts out. The total bend is the deviation δ. Sweep i and δ dips to a minimum exactly when the path is symmetric.

Walkthrough 1 / 4

Step 1 — the prism and the incoming ray at angle i, with the first-face normal.

Angle of incidence i 48°

Prism angle A 60°

i = 48° · A = 60° · e = 48°
deviation δ = 37.2° · near minimum

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