Have you ever used a microscope or a hand held lens? If yes, then you have used lenses. Generally, a big number of people make use of lenses at some point in their lives. One of the major uses of lenses is to focus light. Let’s dig in and find out more.
LEARNING OBJECTIVES
By the end of this topic, you are expected to:
A lens refers to a transmissive optical device which can focus or disperse a beam of light through refraction means. A simple lens is made up of a piece of transparent material. A compound lens on the other hand is made up of more than one simple lens, normally arranged along a common axis. Materials like plastic and glass are used to make lenses. They are ground, polished and molded to the shape that is desired. One of the differences between a lens and a prism is that, a lens is capable of focusing light in order to form an image while a prism only refracts light without necessarily focusing it. Devices that can also focus or disperse radiation and waves apart from the visible light are also known as lenses. These devices include explosive lenses, electron lenses, microwave lenses and acoustic lenses.
CONSTRUCTION OF SIMPLE LENSES
Most of the lenses are spherical in shape. The two surfaces of a lens are parts of a sphere. These surfaces can be either convex or concave. A convex surface refers to that which bulges outwards from the lens while a concave surface refers to that which is depressed into the lens. The line that joins the centers of the spheres that make up lenses is referred to as the axis of the lens. Normally, the lens axis cuts through the center of the lens. Lenses can be cut and ground after manufacturing in order to give them a different size and shape. In such cases, the lens axis may not pass through the physical center of the lens.
TYPES OF SIMPLE LENSES
The classification of lenses is based on the curvature of the two optical surfaces. A lens can be biconvex (or double convex, or just convex) if both surfaces are convex. A lens is said to be equiconvex if both its surfaces have a similar radius of curvature. A biconcave lens is that with two concave surfaces. A Plano-concave or Plano-convex lens is the one where one of the surfaces is flat and the other surface is concave or convex respectively. A meniscus or a convex-concave lens is that which one surface is convex and the other is concave. This type of lens is the one mostly used in corrective lenses.
