Optical Caustics — Reflection

Rays reflecting off curved mirrors form caustic curves (nephroid, cardioid). The caustic is the envelope of reflected rays.

Mirror Shape

Num Rays120

Mirror size130

Source angle180°

Ray opacity0.12

Show caustic

About Caustics

A caustic is the envelope of reflected (or refracted) rays — the curve tangent to every ray in the family.

Circular mirror + parallel rays → nephroid (2-cusped epicycloid).

Circular mirror + point source on circle → cardioid.

Parabola → perfect focus (zero-sized caustic).