A lens is a curved transparent device that bends light, like the lens of eyeglasses or a contact lens you’ll need if the natural lens in your eye needs help. Cameras have a lens, too. Smile!

In an eye, the lens — which is behind the iris — helps focus light on the retina so you can see. It's a lot like the lens in a telescope or camera, which also focuses light and helps form images. You can also use the word lens as a metaphor for how you see things. If you look at sports through the lens of medicine, you might study injuries to players. All these lenses help you see or perceive things.

Definitions of lens
  1. noun
    a transparent optical device used to converge or diverge transmitted light and to form images
    synonyms: lens system, lense
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    compound lens or lens system designed to be free of astigmatism and able to form approximately point images
    anastigmatic lens
    a lens designed to correct astigmatism
    camera lens, optical lens
    a lens that focuses the image in a camera
    compound lens
    a lens system consisting of two or more lenses on the same axis
    condenser, optical condenser
    lens used to concentrate light on an object
    contact, contact lens
    a thin curved glass or plastic lens designed to fit over the cornea in order to correct vision or to deliver medication
    converging lens, convex lens
    lens such that a beam of light passing through it is brought to a point or focus
    crown lens
    a lens made of optical crown glass
    concave lens, diverging lens
    a lens such that a parallel beam of light passing through it is caused to diverge or spread out
    eyepiece, ocular
    combination of lenses at the viewing end of optical instruments
    field lens
    the lens that is farthest from the eye in an optical device with more than one lens
    Fresnel lens
    lens composed of a number of small lenses arranged to make a lightweight lens of large diameter and short focal length
    intraocular lens
    an artificial lens that is implanted into the eye of someone to replace a damaged natural lens or someone who has had a cataract removed
    (optics) a lens that is concave on one side and convex on the other
    eyeglass, monocle
    lens for correcting defective vision in one eye; held in place by facial muscles
    object glass, object lens, objective, objective lens
    the lens or system of lenses in a telescope or microscope that is nearest the object being viewed
    Abbe condenser
    a condenser having 2 or 3 lenses with wide aperture for use in microscopes
    achromatic lens
    a compound lens system that forms an image free from chromatic aberration
    closeup lens
    a photographic lens with a short focal length used to take pictures at short ranges
    portrait lens
    a compound camera lens with a relatively high aperture
    a convex lens that focuses the rays of the sun; used to start a fire
    telephoto lens, zoom lens
    a camera lens that magnifies the image
    fisheye lens, wide-angle lens
    a camera lens having a wider than normal angle of view (and usually a short focal length); produces an image that is foreshortened in the center and increasingly distorted in the periphery
    type of:
    optical device
    a device for producing or controlling light
  2. noun
    electronic equipment that uses a magnetic or electric field in order to focus a beam of electrons
    synonyms: electron lens
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    type of:
    electronic equipment, electronics
    equipment that involves the controlled conduction of electrons (especially in a gas or vacuum or semiconductor)
  3. noun
    biconvex transparent body situated behind the iris in the eye; its role (along with the cornea) is to focuses light on the retina
    synonyms: crystalline lens, lens of the eye
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    type of:
    a fully differentiated structural and functional unit in an animal that is specialized for some particular function
  4. noun
    (metaphor) a channel through which something can be seen or understood
    “the writer is the lens through which history can be seen”
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    type of:
    channel, communication channel, line
    (often plural) a means of communication or access
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