Invisibility Achieved with a Few Clever Focal Points

Invisibility cloaking with lenses

Students at the University of Rochester have developed a clever optical system which allows for limited invisibility thanks to a bit of optic sorcery physics.

Almost all invisibility technologies work by taking light and passing it around the object as if it were never there. The problem is, a lot of these methods are very expensive and not very practical — and don’t even work if you change your perspective from a head on view.

[Joseph Choi] figured out you can do the same thing with four standard achromatic lenses with two different focal lengths. The basic concept is each lens causes the light to converge to a tiny point  in between itself and the next lens — at which point it begins to diverge again, filling the following lens. This means the cloaked area is effectively doughnut shaped around the tightest focal point — if you block the center point of the lens, it won’t work. But everything around the center point of the lens? Effectively invisible. Take a look at the following setup using lasers to show the various focal points and “invisibility zones”.

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Anonymizing clothing


Though much of [citizenFinerran]‘s intent in designing a suit that camouflages the wearer from security camera footage was philosophical, it is designed with a very tangible purpose in mind. The suit does not provide true camouflage (to say nothing of true invisibility), but it does create enough moving visual obstructions to make the wearer completely anonymous on film. More details on this and other invisibility cloaks after the break.

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