Lens that possesses at least one surface that curves inwards. It is a diverging lens, spreading out those light rays that have been refracted through it. A concave lens is thinner at its centre than at its edges, and is used to correct short-sightedness (myopia).
After light rays have passed through the lens, they appear to come from a point called the principal focus. The distance between the principle focus and the lens is the focal length. A more curved lens will have a smaller focal length and will be a more powerful lens. The image formed by a concave lens is virtual, upright, and smaller than the object, and it cannot be projected onto a screen. The lens formula is used to work out the position and nature of an image formed by a lens: 1/u
, where u
are the distances of the object and image from the lens, respectively, and f
is the focal length of the lens.
© RM 2014. Helicon Publishing is division of RM.