Lenses - العلم نور

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الجمعة، 1 مارس 2019

Lenses


Lenses




         Lenses are transmissive optical devices which use refraction to focus or disperse a light beam. A simple lens is made by a single piece of transparent material, these simple lenses can be arranged along a common axis to construct a compound lens. Both glass and plastic can be used to make lenses. By reading this article, you will know more information about lenses i.e. their construction, types and uses.

Construction of simple lenses
         Lenses have two surfaces which are spherical in most cases. There are three forms of these surfaces; convex, concave or planar. The axis of the lens is a line which connects the centers of the two surfaces together.

         There are lenses having surfaces with two different curvature radii which called sphero-cylindrical lenses. Eyeglass lenses is an example of this type of lenses which are used to correct astigmatism in eyes.

         There's another type of lenses which has neither cylindrical nor spherical curvature in one or both of its surfaces called aspheric lenses. These lenses are expensive and difficult to be produced than other standard simple lenses. Images which have less aberration can be produced using these types of complicated lenses.

Types of simple lenses



         There are many types of simple lenses which are classified according to the type of curvature of their both optical surfaces. Lenses are classified as shown below:

·       Biconvex lens: This type of lenses has two convex surfaces. It's called equiconvex lens if the curvature radius of its two surfaces is the same.
·       Biconcave lens: This type of lenses has two concave surfaces.
·       Plano-convex lens: This type of lenses has two different surfaces; one surface is convex and the other one is flat.
·       Plano-concave lens: one of its two surfaces is concave and the other one is flat.
·       Convex-concave lens: it's also called meniscus lens which one of its surfaces is convex and the other surface is concave. It's used commonly in corrective lenses.
         The lens can be classified as positive or converging lens if it is biconvex or plano-convex and the beam of light which passes through the lens will converge to a point or a spot behind the lens. The focal lens (f) equals to the distance between the lens and the spot.

         The lens can be classified as negative or diverging lens if it is biconcave or Plano-concave and the beam of light which passes through the lens will diverge and spread. This beam appears as a point in front of the lens. The focal lens (f) equals to the distance between the lens and this point. It will be negative.

         Convex-concave lens can be also classified as positive or negative. It's positive when having a steeper convex surface and it's thicker at the center. It's negative when having a steeper concave surface and it's thinner at the center.

Uses of Lenses
ü The magnifying glass consists of a single convex lens which is mounted by using a frame having a stand.
ü Lenses are mainly used in the correction of visual impairments such as astigmatism and myopia.
ü Lenses are widely used in imagining systems which used for the production of visual images; cameras, microscopes and projectors.
ü Lenses are used for the production of energy by concentrating the solar energy on photovoltaic cells.
ü Lenses are used by radar systems for the refraction of electromagnetic radiation.




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