In a ray diagram, a concave lens is drawn as a vertical line with inward facing arrows to indicate the shape of the lens.

Draw a ray from the object to the lens that is parallel to the principal axis. Once through the lens, the ray should pass through the principal focus. Draw a ray which passes from the object ...

Paper-thin optical lenses simple enough to mass produce like microchips could enable a new generation of compact optical devices. A team with researchers at the University of Tokyo and JSR Corp.

One example is the question of which lens is right for a given task? There are common lenses like wide-angle, macro, and zoom, as well as lesser-known specialty ones like the anamorphic lens.