convex lens

The passage of light through lenses. The concave lenses diverges a beam of light from a distant source. The convex and compound lenses focus light from a distant source to a point. The distance between the focus and the lens is called the focal length. The shorter the focus, the more powerful the lens.

A convex (or converging) lens causes light rays to refract inwards. A concave (or diverging lens) causes light rays to refract outwards. Convex lenses are used to correct long-sightedness and concave lenses to correct short-sightedness.

Lens that possesses at least one surface that curves outwards. It causes light to deviate inward, bringing the rays of light to a focus, and is thus called a converging lens. A convex lens is thicker at its centre than at its edges, and is used to correct long-sightedness (hypermetropism).

The distance between the lens and the point at which all the rays of light converge (the focal point) is called the focal length. The centre of the lens is known as the optical centre.

At close distance a convex lens forms a magnified virtual image of an object. At further distances the image formed is real, and it can be focused and projected onto a screen behind the lens. The real image formed is upside down, and it can be smaller than, the same size as, or larger than the object depending upon how far the object is from the lens.

Ray diagrams are used to show the position (distance from the lens), size (enlarged or diminished), and nature (real, virtual, inverted, or upright) of an image formed. The lens formula is used to work out the position and nature of an image formed by a lens: 1/u + 1/v = 1/f, where u and v are the distances of the object and image from the lens, respectively, and f is the focal length of the lens.

Common forms of convex lens include the biconvex lens (with both surfaces curved outwards) and the planoconvex (with one flat surface and one convex). The whole lens may be further curved overall, making a concavo-convex or converging meniscus lens, as in some lenses used in corrective eyewear.