Prism Refraction
Holding a prism, glass or crystal in front of the lens to bend light and introduce reflections, flares and repeated fragments.
In depth
The effect is genuinely optical and unrepeatable in software because it is generated before the sensor: reflections carry the scene's own light and colour. It works best with a wide aperture, so the glass itself falls out of focus, and it demands patience since small movements change the result completely.
Examples in practice
A prism angled at the edge of a 50 mm lens at f/1.8 wraps a soft rainbow streak across one side of a portrait.