Technically, the glasses have a distance sensor embedded into the front of the frame and continually adjust the focus of the lenses ... plano-convex or plano-concave lenses, and can do so quickly ...

Instead of a concave lens near the eye, Kepler used a convex ... cheered the coming day when aerial telescopes would have a focus of 1,000 feet and human spectators could marvel at the antics ...

In both cases, rays of light do not focus on the retina so a clear image ... Short-sightedness can be corrected by placing a concave lens in front of the eye, as shown in the diagrams below.

This is because the eye refracts the light and brings it to a focus before it reaches the retina. This is corrected by using a concave or a diverging lens. People who are ‘long sighted’ can ...