"Prism HD"
Light shines into a transparent cylinder dispersing into colours. It internally reflects. Reflected rays cluster, cross to sculpt a dazzling curved caustic surface. Those same rays reflect again to form another caustic. And another and another - spirals of caustic light.

A ray tracing by "Prism HD", an iPad/iPhone App combining optics, accuracy and beauty. "Prism HD", made by Orion Elenzil, allows at the touch of a finger an exploration of refraction and dispersion.

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Circumzenithal arc and more:

Left - Rays strike the top face of a horizontal plate ice crystal. Some externally reflect upwards to form a subsun for those in airplanes. Others leave through a vertical side face making a colourful circumzenithal arc.

Middle - The sun has climbed. The internal angle of incidence is now too steep for all but deep red rays to escape to form a CZA. Instead they totally internally reflect and leave from the crystal lower face to add to the parhelic circle.

Right - A slightly higher sun and there
is no CZA.

The Humble Sundog:

  Rays meet a horizontal plate crystal. Some reflect into the parhelic circle. Some leave a face inclined at 60° to the first to form a prismatic sundog or 22° parhelion.

  What of those that reflect internally to emerge at different angles. What do they form?


Orders of Rainbows:

Sunlight from far right hits a raindrop. Prism HD's attenuation control is turned down so that we see many internal reflections and higher orders of rainbows.

Rainbows get wider and fainter as their order increases. The long sought 3rd and 4th order bows have recently been photographed for the first time.