Question

What is lenses

Answer 1

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. Convex lenses

In a convex lens the glass (or plastic) surfaces bulge outwards. A convex lens is also called a converging lens because it makes parallel light rays passing through it bend inward and meet (converge) at a spot just beyond the lens known as the focal point.

Concave lenses

A concave lens is exactly the opposite with the outer surfaces curving inward, so it makes parallel light rays curve outward or diverge. That's why concave lenses are sometimes called diverging lenses.