Concave Lens

Since the beginning of time, human beings have been able to do some pretty remarkable things. The lens is one of the major discoveries made by humans. Although one can’t say when or how the lens was discovered, it is clear that at some point in the past, ancient people realized that they could manipulate light using a piece of glass. Humans used lens to make distant objects appear nearer, small objects appear larger and blurry objects appear clear (i.e. magnifying glasses and corrective lenses). Lenses used to accomplish these tasks fall into two categories of simple lenses as Convex and Concave Lenses.

What is a Concave Lens?

A concave lens is a type of lens that diverges a straight light beam coming from the source to a diminished, upright, virtual image is known as a concave lens. It can form both real and virtual images. Concave lenses have atleast one surface curved inside. A concave lens is also known as a diverging lens because they are shaped round inwards at the centre and bulges outwards through the edges, making the light diverge on it. They are used for the treatment of myopia as they make faraway objects look smaller than they really are.

  • The point in the lens where the light refracts and diverges is known as the principal focus.
  • The distance between the principal focus and the centre of the lens is known as the focal length.

If the thickness of the lens is less compared to the radius of the arc, then the lens is called a thin lens. The optical power of the lens is given by the formula:

\(\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\)

where f is the focal length

v is the distance of the image from the centre

u is the distance of the object from the centre

Similarly, the magnification of the image is given by the equation,

\(M=\frac{h_{i}}{h_{o}}=\frac{v}{u}\)

where M is the magnification

hi is the height of the image

ho is the height of the object

Image Formation in Concave Lens

  • When an object is placed at infinity, a virtual image is formed at the focus. The size of the image is much smaller as compared to that of the object.
  • When an object is placed at a finite distance from the lens, a virtual image is formed between the pole and focus of the convex lens. The size of the image is smaller as compared to that of the object.

Uses of Concave Lens

Some uses of the concave lens are listed below:

Used in Telescope

Concave lenses are used in telescope and binoculars to magnify objects. As convex lens create blurs and distortion, telescope and binocular manufacturers install concave lenses before or in the eyepiece so that a person can focus more clearly.

Used in Eye Glasses

Concave lenses are most commonly used to correct myopia which is also called nearsightedness. The eyeball of a person suffering from myopia is too long, and the images of faraway objects fall short of the retina. Therefore, concave lenses are used in glasses which corrects the shortfall by spreading out the light rays before it reaches the eyeball. This enables the person to see far away objects more clearly.

Used in Peepholes

Peepholes or door viewers are security devices that give a panoramic view if objects outside walls or doors. A concave lens is used minimizes the proportions of the objects and gives a wider view of the object or area.

To know more uses of a concave lens, click here.

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