Question

What is lens ? Why it's use?

Answer 1

Lens is the combination of double convex or concave mirror.A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis

Uses..
Most high quality cameras, telescopes and binoculars use concave lenses to improve the quality of the images they provide. Microscopes and reflecting telescopes make use of a concave mirror, a plane mirror, and a convex lens, while refracting telescopes use two convex lenses