A lens is an optical device that works on the principle of refraction. Based on the type of curved surface of the lens they can be classified into two types concave and convex lens. As the name suggests a concave lens has a concave surface on both sides, thin at the center and thick at the edges. A convex lens on the other hand is thick at the center and thin at the edges. In this article, we discuss 10 differences between concave and convex lenses.
What is a concave lens?
A concave lens has surfaces curved inwards. It is a diverging lens that diverges a straight beam of light to produce a diminished and upright image. It can form both real and virtual images. The shape of the lens is in such a way that it curves inwards at the center and bulges outwards through the edges. They are used to treat myopia. A concave lens is used in applications where light needs to diverge like a flashlight, laser devices, telescopes, etc.
What is a convex lens?
A convex lens has two spherical surfaces curved outwards. A convex lens converges light to the focal point. It is relatively thick across the middle and then towards the edges. Convex lenses are used in applications where far-off objects need to be focused like magnifying glasses, eyeglasses, optical microscopes, projectors, cameras, etc.
Difference between convex and concave lenses
| COMPARISION | CONCAVE LENS | CONVEX LENS |
| Definition | A concave lens is a diverging lens that sends a straight light beam in different directions. | A convex lens is a converging lens where the parallel beam is converged at a particular point. |
| Diverging/converging | They are also called diverging lenses. | They are also called converging lens. |
| Surface | A concave lens has surfaces curved inwards | A convex lens has two spherical surfaces, curved inwards. |
| Focus | It has a real focus. | It has a virtual focus. |
| Focal length | The focal length of a concave mirror is negative. | The focus length of a convex mirror is positive. |
| Thickness | A concave lens has thick edges and is thin in the middle. | A convex lens has thin edges and is thick in the middle. |
| Image formation | The image formed in a concave lens is virtual, upright, and small in size. | The image formed in a convex lens can be small or large in size. The image formed is real and inverted. |
| magnification | A concave lens’s magnification is less than one. | A convex lens’s magnification is less than one for a virtual image and greater than one for a real image. |
| Application in spectacles | A concave lens is used for people suffering from myopia. | A convex lens is used for people suffering from hypermetropia. |
| Application | A concave lens is used in objects like flashlights, cameras, and lasers. | A convex lens is used in objects like magnifying glasses, microscopes, etc. |
Difference between concave and convex lenses based on the application in spectacles
A concave lens is used in treating myopia whereas a convex lens is used to treat hypermetropia. The difference in the application of convex and concave lenses is due to the converging or diverging nature of the lens.
A concave lens is diverging in nature. Sometimes the eye focuses on the light coming into it just before the retina. It has to be adjusted so that the image forms on the retina. The diverging lens(concave lens) diverges the light so that the image forms on the retina.
A convex lens is converging in nature. When the eye lens is focussing the image beyond the retina, then a convex lens is used to focus the image on the retina.
You can read about more applications of convex lenses and concave lenses.
Difference in image formation between the concave and convex lens
The image formed in a concave lens is virtual, upright, and diminished in size.
The image formed in a convex lens can be diminished or magnified and is real and inverted.
