The first refracting telescope was invented by the Dutch spectable maker, Hans Lippershey, in 1608. It consisted of a convex and concave lens in a tube, and the combination of these two lenses magnified three or four times of the original object. Later, it was developed to view farther objects, but the clarity was restricted by false colour effects due to poor quality of available glass. The object-glass, the main lens responsible for collecting the light, did not bend all wavelengths equally; and this resulted in the red part of the light-beam being brought to a focus at a greater distance from the object-glass. Even if the quality of glass was good, the telescope could still not obtain very far away objects, such as the satellites of Jupiter. A few years later, Galileo discovered his own telescope which was good enough to see Jupiter's moon. However, one problem occured. The Galilean telescope produced inverted images. As early as 1611, Johannes Kepler pointed out that a telescope could also be made by combining a convex objective and a convex ocular. He pointed out that such a combination would produce an inverted image but showed that the addition of yet a third convex lens would make the image erect again. Because the more lenses the more optical defects multiplied, the Galilean telescope was replaced by ones with more convex lenses. Soon, longer telescopes were developed. A typical astronomical telescope is the one made by Christian Huygens in 1656. It was 23 feet long with its objective had an aperture of several inches and magification about 100 times and its field of view of 17 arc-minutes. Telescopes nowadays are even more advanced. New technology continually improves the magnification so that we can explore the outter universe.
Galileo and his telescope