Scratched glasses give perfect vision for any eyesight — if by scratched you mean engraved and by perfect you mean in-focus but low-contrast:
Zeev Zalevsky at Bar-Ilan University in Ramat Gan, Israel, has developed a technique to turn a standard lens into one that perfectly focuses light from anything between 33 centimetres away and the horizon.
It involves engraving the surface of a standard lens with a grid of 25 near-circular structures each 2 millimetres across and containing two concentric rings. The engraved rings are just a few hundred micrometres wide and a micrometre deep. “The exact number and size of the sets will change from one lens to another,” depending on its size and shape, says Zalevsky.
The rings shift the phase of the light waves passing through the lens, leading to patterns of both constructive and destructive interference. Using a computer model to calculate how changes in the diameter and position of the rings alter the pattern, Zalevsky came up with a design that creates a channel of constructive interference perpendicular to the lens through each of the 25 structures. Within these channels, light from both near and distant objects is in perfect focus.
“It results in an axial channel of focused light, not a single focal spot,” Zalevsky says. “If the retina is positioned anywhere along this channel, it will always see objects in focus.”
Zalevsky has fitted one of his lenses to a cellphone camera to confirm the extended focus effect, and he has also tested the lenses on 12 volunteers (Optics Letters, vol 35, p 3066). He has now co-founded a company, Xceed Imaging, to develop the technology.
The approach is not without its problems, though: the interference pattern tends to cancel out some of the light passing through the lens, which reduces the contrast of images viewed through it.