Posted on 25th August 2012
Without going into too much of the detail, lenses focus light but altering the direction and speed of light rays passing through the material. The amount of material a light ray passes through and the curvature of the 2 surfaces of the lens affect the direction light. Varying the thickness and curvature of lenses in different parts of the lens bend rays differently, focussing them or spreading them out as required.
All this bending of light rays causes lots of aberrations which are the names of unwanted optical distortions. Some of these you will have heard of eg defocus (such as in long and short sight) and astigmatism; but there are lots of others you probably won’t have eg coma, Petzval field curvature and so on. All these aberrations degrade the quality of the final image. We design your glasses lenses with special combinations of thickness and curvature to minimise these aberrations but you can eliminate them entirely.
If you are wearing glasses, look out through the edge rather than the centre of your lens at something white like your ceiling. You might see some coloured fringes, look through the other edge and you might see the fringes are now a different colour. This is a type of aberration called ‘chromatic aberration’.
If you’re quaffing a glass of vino, hold up the empty glass to something square behind it like a picture frame. The frame is all distorted and mishapen, this is an aberration called ‘distortion’.
This new Harvard lens has only one surface and is effectively 2 dimensional (60 nanometres thick) and not very like a lens as you would think of it. It uses tiny little V shaped ‘antennas’ made of a layer of gold on a silicone wafer. The little Vs alter the speed of light waves instantly and they don’t require passage through a material to change direction. Altering the size and position of these ‘V’s across the surface alters the lens properties.
It’s quite obvious how a such a thin lens would be helpful in any optical system (including glasses) from a physical point of view, but the lack of aberrations is also very exciting. Super vision lenses are within our grasp!
16th September 2020
Some patients might be interested in this article where Ian Cameron shares his thoughts on prescribing. We were one of the first practices to have an optometrist who could prescribe medication to pati...Read more
26th May 2020
Last week we provided advice on how to prevent your child suffering from digital eyestrain. This week, we're looking at adults, in particular those working from home (most of us at the moment!). Ian...Read more