Such a piece of glass is referred to as a lens. A lens is merely a carefully ground or molded piece of transparent material which refracts light rays in such as way as to form an image. Lenses can be thought of as a series of tiny refracting lenses, each of which refracts light to produce their own image. When these prisms act together, they produce a bright enough image focused at a point. There are a variety of types of lenses.
Lenses differ from one another in terms of their shape and the materials from which they are made.
Our focus will be upon lenses which are symmetrical across their horizontal axis - known as the principal axis . In this unit, we will categorize lenses as converging lenses and diverging lenses. A converging lens is a lens which converges rays of light which are traveling parallel to its principal axis. A diverging lens is a lens which diverges rays of light which are traveling parallel to its principal axis. A double convex lens is symmetrical across both its horizontal and vertical axis.