A concave lens, also known as a diverging lens or a negative lens, is a lens with at least one surface that curves inward, causing light rays passing through it to diverge or spread apart. Concave lenses are thinner at the center and thicker at the edges, giving them a curved-in shape.

Here are some key characteristics and properties of concave lenses:

1. Focal Point: A concave lens has one focal point, which is located on the same side as the incoming parallel rays. The focal point is the point where the outgoing rays appear to originate when extended backward. Unlike convex lenses, which have real focal points, the focal point of a concave lens is virtual.
2. Principal Axis: The principal axis of a concave lens is an imaginary line passing through the center of the lens, perpendicular to its surfaces. It serves as a reference line for analyzing the behavior of light rays.
3. Diverging Properties: When parallel rays of light pass through a concave lens, they refract and diverge, appearing to originate from the virtual focal point. The rays continue to spread apart after passing through the lens. This divergence is why concave lenses are called diverging lenses.
4. Image Formation: Concave lenses always produce virtual, upright, and reduced images, regardless of the object’s position. The image formed by a concave lens appears on the same side as the object and is formed by the diverging rays of light.
5. Correcting Vision Defects: Concave lenses are commonly used in correcting nearsightedness (myopia). In nearsighted individuals, light rays from distant objects focus in front of the retina, resulting in blurry vision. By introducing a concave lens in front of the eye, the light rays are diverged before entering the eye, helping to shift the focal point backward onto the retina, thereby correcting the vision.

It’s worth noting that the power of a concave lens is expressed in negative diopters. The greater the negative value, the more diverging power the lens possesses.

Concave lenses have various applications, including eyeglasses for nearsightedness, optical devices, scientific experiments, and optical systems that require the divergence of light. They play a crucial role in vision correction and the manipulation of light in different optical setups.