Notes about optics

June 23, 2011 permalink


Research continues on whether humans (and other animals) have the ability to perceive magnetic fields:

Many birds have a compass in their eyes. Their retinas are loaded with a protein called cryptochrome, which is sensitive to the Earth’s magnetic fields. It’s possible that the birds can literally see these fields, overlaid on top of their normal vision. This remarkable sense allows them to keep their bearings when no other landmarks are visible.

But cryptochrome isn’t unique to birds – it’s an ancient protein with versions in all branches of life. In most cases, these proteins control daily rhythms. Humans, for example, have two cryptochromes – CRY1 and CRY2 – which help to control our body clocks. But Lauren Foley from the University of Massachusetts Medical School has found that CRY2 can double as a magnetic sensor.

Vision is amazing, even more so when you take into account the myriad other things that animals and insects can detect beyond just our “visible” EMF spectrum. See also: box jellyfish with their surprisingly complex (and human-like) set of 24 eyes.

September 12, 2009 permalink

Binocular Diplopia and the Book of Kells

How did reclusive monks living in the year 700 or 800 AD draw the intricate lines of the Book of Kells, rendered by hand at sub-millimeter resolution (about the same level of detail as the engraving work found on modern money), hundreds of years before optical instruments became available, hundreds of years before the pioneering visual research of Alhazen? According to Cornell paleontologist John Cisne’s theory, their trick was in the detail and pattern: by keeping their eyes unfocused on the picture plane, the monks could superimpose their linework and judge the accuracy against the template using a form of temporary binocular diplopia (sort of like willing yourself to view a stereograph or one of those Magic Eye posters).

That’s amazing.

August 8, 2009 permalink

Transformation optics as misdirection

From Nature, Optics: All Smoke and Metamaterials (subscription might be required, actual research publication available from the American Physical Society):

Seeing is believing — a naive assumption in the case of an illusion device proposed by Lai and colleagues at the Hong Kong University of Science and Technology, and described1 in Physical Review Letters. The new device has the power to ‘act at a distance’ and therefore covertly alter an object’s appearance such that it has no apparent physical connection to the light scattered by the object — although this becomes increasingly difficult to achieve the farther the illusion device is from the object. Lai and colleagues1 outline a mathematical formalism proving that it is theoretically possible to grab the rays of light emitted by a given object and to reconstruct them so that they seem to come from a completely different object.

Using metamaterials with refractive indexes less than zero to disguise the origin or content of reflected light. Not sure that I entirely understand this idea, but it’s sort of like the fabled “cloaking device”, except that instead of rendering an object invisible it actually renders it as a different object. Things will be weird fifty years from now.