Telescopes are instruments for observing objects that are at a practically infinite distance, such as celestial bodies.
They fall into two large categories: refracting telescopes, having a converging objective, and reflecting telescopes, having a concave mirror as their objective.
The name of telescope is normally applied to reflecting telescopes while refracting telescopes are sometimes referred to as astronomical telescopes (cannocchiali astronomici in Italian).
Kepler's telescope was invented in 1611 by Johannes Kepler (1571-1630) who, in his Dioptrice, demonstrated that the system used in Galileo's telescope was not the only one possible and described one in which the diverging eyepiece lens was replaced by a convergent one.
It appears that the Jesuit Christoph Scheiner (1575-1650) was the first, some time around 1613, to built a telescope like the one described by Kepler with a converging objective having a long focal length and an eyepiece, it too convergent, having a short focal length. ...continues