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A lens is a piece of glass or other transparent material with curves that concentrates or disperses the light serves as a great part of any optical instrument. It is used to divert the direction of the light rays. The refracted ray is affected by the curvature and thickness of lenses. This section gives an idea about different types of lenses in detail and optical instruments which is used used to improve the vision.


Lens definition

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A lens is a piece of transparent glass that is bounded by two spherical surfaces. Basically there are of two types
The convex lens is thick at the center but thin at the edges that are of types . The concave lens is thinner at the center than its edges and are of the types namely double convex lens, plano-convex and concavo-convex lens.

Lens Types

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The main categories among the lens are concave and convex lenses. In concave lens, plano-concave and double concave or biconcave lenses are present. Plano concave means, one surface is plane and the other one is curved inward. In the case of convex lens, plano-convex and double convex or biconvex lenses are there. In plano-convex one surface is plane and other surface is bulged. But in biconvex, two surfaces are bulged.

Concave Lenses Types

Lens Focal Length

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Generally focal length of an optical system is a measure of how strong they diverge or converge the light rays. Focal length is the distance between the focal point and the center of lens. Focal point is nothing but the point at which the light ray converges or diverges. Focal point is different in case of different lenses. In the case of concave lens, focal point is in front of the lens; whereas in the case of convex lens, focal point is behind the lens.

Converging Lens

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Converging lenses are generally known as convex lenses. A convex lens is nothing but the transparent medium like glass, which is curved outward and the thickness is decreasing along the edges. When light rays are incident on this lens, it get refracted to a single point due to the change in the medium. This point is known as the focal point. Converging lens always forms virtual images.

Diverging Lens

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Diverging lenses are commonly called as concave lenses. In this case, the transparent material is curved inward and the thickness is increasing along the edges. This lens produces real as well as virtual images according to the object's position. If the light rays are incident on the lens, it get refracted. When we extend these rays it appears to come from a single point. This is known as the focal point of a concave lens.
An optical instrument enhance the ability to see object, some of which may no longer exist. With microscopes, we can see detailed images of tiny objects. Telescopes, microscopes and cameras are the examples of optical instruments which enhance the ability of vision. The common characteristics of these instruments are, it consists of lenses or mirrors or a combination of the two to reflect or refract light.
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