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Friday 25 Nov 2022Four geometrical-optics illusions

Michael Berry - University of Bristol

Newman Red 12:30-13:30

Many centuries after the laws of geometrical optics were established, they still have nontrivial and varied applications. Illustrating this are some illusions:

• Mirages, and Raman’s error. Understanding why he denied the applicability of geometrical optics requires careful exploration of the continuum limit of a discretely-stratified medium

• Oriental magic mirrors and the Laplacian image. The optics of these ancient objects involves the regime of pre-focal brightening, and the transmission analogue raises a challenge for freeform optics.

• The squint moon and the witch ball. The moon sometimes appears to point the wrong way because we perceive the sphere of directions as a distorted ‘skyview’, on which geodesics appear curved. This can be conveniently viewed and analysed by viewing the sky in a reflecting sphere.

• Distorted and topologically disrupted reflections in curved mirrors. The mirror- reflected rays from an object form caustic surfaces in the air. Images of such objects are organised by those points whose caustics intersect our eyes.

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