When a "Telescope" term come in mind, we always think of that tube with the big lens and the small one we look in. Though its inventor may be lost in history, this early kind of telescope is called a "Galilean" or simple refractor. The Galilean refractor consists of two lenses: a convex (curved outward) lens held in front of a concave (curved inward) lens a certain distance away. As you know, the telescope’s front lens is called the objective, while the other is referred to as the eyepiece, or ocular.
