Have you ever snapped a photo or looked through a microscope? If your answer is yes, then you have used an optical device. There are many kinds of optical devices. Cameras and microscopes are two examples. Others are projectors, binoculars, telescopes, and even eyeglasses. Every optical device is different. But they all have one thing in common. Each one has at least one lens.
What is a lens?
A lens is a transparent substance that bends or refracts light in a definite way. Most lenses are made of glass. Many lenses are made of plastic. Most lenses have one or two curved surfaces. There are two main types of lenses: convex and concave. A convex lens is thicker at the centre than at the edge. It magnifies or makes things look bigger. A convex lens brings together, or converges, light rays. The point where the light rays meet is called the focal point.Light that passes through a convex lens can be focused on a screen or other surface. This forms an image of the object that gave the light. Convex lenses are used in projectors and cameras. A concave lens spreads-out light rays. They cannot form an image on a screen. Concave lenses are often used together with convex lenses. They help the convex lenses give sharper images.
Most eyeglass lenses have combinations of concave and convex curves.
