A lens can be described as an optical device that transmits and refracts the incident beam by converging or diverging it. A simple lens consists of a single optical element, while a compound lens is an array of simple lenses arranged in such a way that they have a common axis.
Single lenses often lead to aberration or distortion of the image. Aberrations can be corrected to a large extent by using compound lenses in place of simple lenses. Therefore, designing of lenses need to be done with utmost care and precision in order to keep the aberration to bare minimum. The working principle, construction, types and applications of lenses are described in the sections below.
Single lenses are made up of two precisely regular opposite surfaces. These surfaces are curved; this curvature causes the incident beam to converge at a single point called the focal point. The distance at which the focal point is formed behind the lens gives the focal length of the image. The size of the image formed by the lens depends on the focal length of the lens.
Construction and Types of Lenses
Most lenses are spherical lenses and are made of two surfaces that are part of two spheres. Lenses are often cut or ground to impart a different shape. Lenses are broadly classified as single and compound lenses based on their construction. Detailed classification of lenses is given below:
- Single lenses – further classified into biconvex, plano-convex, positive meniscus, negative meniscus, plano-concave and biconcave.
- Compound lenses – array of single lenses
- Cylindrical lenses – have curvature in one direction
- Fresnel lenses – its optical surface is broken into narrow wings
- Super lenses – made from meta materials with a negative refraction index
- Lenticular lenses – arrays of micro lenses.
Some of the main applications of lenses are provided below:
- Vision impairment treatment
- Binoculars, microscopes and projectors
- Radio astronomy and radar systems.