focal length

noun Optics.

the distance from a focal point of a lens or mirror to the corresponding principal plane. Symbol: f
the distance between an object lens and its corresponding focal plane in a telescope.
Also called focal distance.

Origin of focal length

First recorded in 1745–55

Words nearby focal length

focal depth, focal distance, focal epilepsy, focal glomerulonephritis, focal infection, focal length, focal necrosis, focal plane, focal point, focal ratio, focal reaction

British Dictionary definitions for focal length

focal length

focal distance

noun

the distance from the focal point of a lens or mirror to the reflecting surface of the mirror or the centre point of the lens

Medical definitions for focal length

focal length

n.

The distance from the surface of a lens or mirror to its focal point. focal distance focus

Scientific definitions for focal length

focal length
[ fō′kəl ]

The distance between the optical center of a lens or mirror to its focal point.

Cultural definitions for focal length

focal length

The distance between the focal point of a lens (that is, the point at which the lens will focus parallel rays of light) and the lens itself.