A lens is a transparent piece of glass or plastic that is curved and used to bend (refract) light rays. There are mainly two types of lenses:
Convex lens: Thicker in the middle and thinner on the edges, a convex lens can form real images by converging light rays when the object is outside the focal point and virtual images when it is closer than the focal length.
Concave lens: Forming only virtual images, a concave lens is thinner at the centre and thicker at the edges, diverging light rays. It has a virtual focal point instead of a real one, and rays appear to originate from it.
Convex Lens
- A convex lens is thicker at its centre and thinner at its edges, bulging outward like the exterior of a sphere.
- It is also known as a converging lens because it focuses parallel rays of light that pass through it.
- A convex lens converges parallel rays of light to a focal point on the opposite side of the lens from the light source.
- It can form real and inverted images when objects are placed beyond its focal point, and it can create virtual and upright images when objects are placed between the lens and its focal point.
- Convex lenses are commonly used in magnifying glasses, cameras, telescopes, and binoculars to focus and magnify distant objects.
- They are also used in eyeglasses to correct farsightedness (hyperopia) and presbyopia.
Types-
Biconvex Lens: The lens has a shape, on both sides, bulging towards the centre. It is commonly used in magnifying glasses and simple camera lenses.
Plano Convex Lens: This lens has one side (plano). The other side is curved outward. It is designed to focus rays to a specific point and is often found in optical instruments and projectors.
Concavo Convex: This lens has a convex face and a concave face. In this lens convex face has a smaller curvature.
Concave Lens
- A concave lens is thinner at its centre and thicker at its edges, curving inward to create a hollow or dented appearance.
- It is known as a diverging lens because it spreads out parallel rays of light that pass through it.
- A concave lens causes parallel rays of light to diverge as if they originated from a virtual focal point on the same side as the light source.
- It can only produce virtual and diminished images when objects are placed on the same side as the virtual focal point.
- Concave lenses are used in eyeglasses to correct nearsightedness (myopia) and in certain scientific instruments and devices to spread out light or correct optical aberrations.
Types-
Biconcave Lens: The lens curves inward on both sides, causing it to become thinner towards the centre. This design disperses rays and creates virtual images. It is commonly used in eyeglasses for nearsightedness.
Plano Concave Lens: Similar to the lens, this one also has one side but curves inward on the other side. It diverges light. Finds application in specific optical systems, like beam expansion setups.