It is said that Nero used a ruby as a magnifying glass. During the Middle Ages it was quite usual for short-sighted scholars to use spectacles for reading. In about 1600, a Dutchman called Liepperhey built the first telescope worthy of the name. Later, Galileo built others for himself and pointed them at the sky. The era of modern Science had begun.

This is another convergent lens with a much shorter focal distance than the main lens, where the observer places their eye. It acts as a magnifying glass on the image formed by the main lens. Modern eyepieces can be made up of many simple lenses.

It is the convergent lens where light enters the instrument. In modern telescopes there is a combination of two or more lenses. There are also telescopes which use a concave mirror. The lens serves to produce a tiny inverted real image of the distant object we are viewing.