Joseph Choi and John Howell from the University of Rochester have published a paper showing how to create an invisibility cloak using four standard optical lenses which can be purchased for a hundred dollars.
The invisibility cloak is a staple in science fiction and fantasy. Scientists have taken stabs at making this fiction become reality, but this has mostly involved using high tech expensive material to bend light around objects. This effect doesn’t work at all angles, so if the observer moves, the hidden object will come back into view. Choi and Howell’s four lens invisibility cloak works at all angles in front of the lenses and is relatively cheap to set up. They have even published simple instructions on how to do this yourself.
Basically you just need to buy four lenses: two lenses with the same focal length (f1) and two with a focal length (f2). They need to be set up in mirror image, so f1 is the first lens, f2 is the second, f2 is the third and f1 is the fourth. The first pair of lenses (lens 1 and 2) should be separated by a distance that is equal to the sum of their focal lengths (f1+ f2). The second pair of lenses (lens 3 and 4) should be separated by the same distance. Lens 2 and 3 should be separated by the distance calculated in this equation: t2=2 f2 (f1+ f2) / (f1— f2).
It makes more sense in this very cool video of the cloak in action: https://www.youtube.com/watch?v=vtKBzwKfP8E
This technology can be scaled up by using bigger lenses to hide bigger objects. The University of Rochester has filed a patent for this version of an invisibility cloak.
The Scientific Paper (free and open access on the awesome physics pre-print server arXiv.org):
Choi and Howell. Paraxial Ray Optics Cloaking. Optics Express. 2014.