He invented the Keplerian telescope

One of the interesting facts about Johannes Kepler is that he invented the Keplerian telescope. Johannes Kepler significantly enhanced Galileo's conventional refracting telescope design in 1611. In essence, Kepler chose to utilize a convex lens as the telescope's eyepiece rather than a concave lens. The Kepler design's key benefit is that it concentrates the light beams coming from the eyepiece.

Using a telescope that was a loan from Duke Ernest of Cologne, Kepler also started doing theoretical and experimental studies on telescopic lenses. In September 1610, the resulting manuscript was finished, and Dioptrice was released in 1611. Kepler outlined the theoretical underpinnings of the biconvex and double concave divergent lenses and how they were combined to produce the Galilean telescope in this work. The ideas of real and virtual images, vertical vs inverted images, and the impact of focal length on magnification and reduction are all similar. Additionally, he proposed a better telescope now known as a telescope or Keplerian Telescope in which the use of two convex lenses could yield magnifications higher than those achieved by using two convex lenses in conjunction with Galileo's concave lens.

The Keplerian telescope considerably decreases eye pain and offers a far wider field of view. The upside-down position of the viewer is the only drawback. The new design, however, permits greater magnifications, but obtaining them requires a huge lens.