Fast Electrically Focus Tunable Lens

When you are reading this post, when you are looking around, your eyes will automatically focus on the spot by reshaping our eye lens. With glass lenses as used in optics, you can achieve that only with moving a lens-system back and forward.

Optotune has introduced now a commercial tunable lens which reshapes its surface and allows continuously focusing between 20mm to 120mm by an external voltage. In the manual version you can even go from -40mm to 40mm, so from concave to convex!




This could find applications in material processing, ophthalmology or microscopy. For further applications have a look at their application homepage

Interesting is also the microscopy application:



Have fun!

Modelling an artificial eye with a CCD camera: see how they see!

In September I attended the "IX Reunión Nacional de Óptica" (Spanish National Optics Meeting); one of the posters presented there by the Optics Group from Zaragoza (J. Ares, V. Collados, J. Arines and A. Sánchez-Cano) was "Adiestramiento de la refracción subjetiva con ojos simulados mediante cámaras web". In this communication, the authors reported a system based on a CCD camera to simulate an artificial eye that is used to teach optics and optometry.

Let's start by explaining how the eye works.

Figure 1: Scheme of the eye

In the image an schematic view of an eye is represented; in a very simple model, we can consider the eye as a system formed by a refractive surface, the cornea, and the lens. In a normal eye, the light is focused at the fovea and the image is well-defined. When a person suffers from myopia, light is focused before the fovea; when a person suffers from long-sight, image is formed after the fovea.

Now, how can it be modelled with a web camera? Well, basically the webcam is a CCD sensor with a lens. If we replace this lens by a 35mm focal length lens (typical value for a human eye) and a diaphragm (which will act as a pupil), we can build an artificial eye.

Once, the webcam is ready you can try how people see. Ask for example for a pair of glasses and place them immediately before the webcam. If the person who has lent you the glasses suffers from myopia, you will see a blurred image: this is how this person sees without glasses (or better said, the opposite to the way this person sees: it corresponds to the vision of a long-sighted person with the same gradation):

Figure 2: Pictures from the first row represent a near-sighted eye without (left) and with (right) glasses to correct the myopia. The second row corresponds to a normal eye (ie., the webcam) without (left) and with (right) the same lenses as used in the previous case.

Pink is not a colour

Have a look at the visible spectrum; you can see many colours: red, blue, green, yellow... but what about pink?

You can not find it in the spectrum... but then, why do we see it? Basically, we could say that the reason is just the difference between wavelength (property of waves) and colour (asigned by the brain).

When the eye perceives just one wavelength (for example 600 nm), our brain identifies the colour of that wavelength (in this example, red).

But, what happens if the eye receives light of more than one wavelength? In this case, the colour interpreted by the brain is usually the sum of the input responses on the retina, i.e. the colour halfway between them... except when the wavelengths come from both ends of the light spectrum at once (i.e. red and violet light).

In this case, the colour halfway would be green (not very representative of the mixture), so the brain simply invents a new colour halfway between them: pink (or magenta, according to its official name).

This post has been adapted from http://www.biotele.com/magenta.html. You can find there a extended version.

Prof. Sánchez Ramos awarded Best Invention of the Year

Spanish researcher Professor Celia Sánchez Ramos, has been awarded in Geneva with a prize for the Best Invention of the Year given by the World Intellectual Property Organisation.
Prof. Sánchez Ramos, who is a researcher at the Complutense University in Madrid (UCM), invented a light filter for contact lenses to protect the retina and prevent blindness.
Between 15% and 20% of the light spectrum consists of harmful colours for us (blue and violet), which destroy the retina neurons leading to a degeneration into the macula (DMAE); the fovea, a part of the retina structure, protects us from these colours. Prof. Sánchez Ramos proved that this part of the spectrum could be blocked by inserting a yellow filter into the lenses.
In spite of being yellow, the lens does not vary the perception of the person.
To test the efficiency of the lens, the researcher carried out a experiment with rats exposed to different light types and rabbits which had been previously operated for cataracs.
Nowadays, the UCM is carrying out a clinic trial in 23 hospitals with people operated for cataracs.