minimum deviation
The minimum total deviation, relative to neighboring deviations, of an incident wave (or ray) transmitted by a bounded, optically homogeneous body (e.g., prism, ice crystal, raindrop).
The corresponding angle between the direction of the incident wave and that transmitted by the body is the angle of minimum deviation. Rainbows and arcs of 22° are, according to geometrical optics, formed at angles of minimum deviation.
