equipment that involves the controlled conduction of electrons (especially in a gas or vacuum or semiconductor) | a transparent optical device used to converge or diverge transmitted light and to form images |
| electronic equipment that uses a magnetic or electric field in order to focus a beam of electrons |
| biconvex transparent body situated behind the iris in the eye; its role (along with the cornea) is to focus light on the retina |
| (metaphor) a channel through which something can be seen or understood |