Lenses In Optics

What Are Lenses?

The most apparent distinction between mirrors and lenses are that mirrors reflect light rays (light bounces back) while light rays are refracted (pass-through) through a lens. A mirror will have only one focal point, which is in front of the mirror. A lens has two focal points each on either sides.

There is a similarity between the concave mirror and convex lens that is, in both a concave mirror as well as a convex lens the light converges at the focal point. Similarly, the convex mirror and concave lens diverge the light at the focal point.

Types Of Lenses

The classification of a lens depends on how the light rays bend when they pass-through the lens. The two main types of lenses are:

  • Convex Lens (Converging)
  • Concave Lens (Diverging)

Convex lenses are thick in the middle and thinner at the edges. A concave lens is flat in the middle and thicker at the edges. A convex lens is also known as the converging lens as the light rays bend inwards and converge at a point which is known as focal length. On the other hand, the concave lens is also known as a diverging lens because it bends the parallel light rays outward and diverges them at the focal point.

Simple lens and compound lens are the two classifications of lenses. Simple lenses are different from compound lenses based on their surface of curvature. Following are the different types of simple lenses.


Compound lenses are those constructed out of a combination of different simple lenses. The lens types used to build a compound lens may have different refractive indices and other properties. The placement of lenses are such that they lie on a single axis, and properties like focal length are calculated again for the new compound lens.

Other Lens Types are:

  • Cylindrical – curvature in one direction
  • Fresnel – narrow ring-like surface
  • Lenticular – a group of microlenses
  • Gradient Index – flat surfaces but with varying refractive indices
  • Axicon – conical surface

Interested to learn more about the lens, below are the links:

Applications Of Lens

What do magnifying lens, your eye and binoculars have in common? They all use convex lenses. And have any of you wondered why people look so weird when you see them through a peephole? That’s because the glass used there isn’t a normal one. It is a concave lens. Convex lenses are used to correct farsighted vision problems.

Similarly, concave lenses are used to correct nearsightedness. Compound microscopes and telescopes use both convex and concave lenses. Using combinations of convex lenses may create blurry images. A concave eyepiece is used to correct this problem. Even in cameras at times a combination of concave and convex lenses are used. The use of concave lenses is essential in lasers. The actual light ray is highly specific, which may damage equipment where it is used (like CDs and scanners). The diverging lens rectifies this issue. Concave lenses also find application in flashlights where the light beam diverges for broader area coverage.

Learn about lenses and their real-life applications with experienced tutors here at BYJU’s.

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