Johannes Kepler improves on the Galilean telescope design. Due to a flawed design, most notably an inefficient lens shape and narrow field of view, most images observed with a Galilean telescope were distorted and out of focus. Magnification was also roughly limited to 30 times normal size. Kepler improved upon Galileo's design by using a convex lens for the eyepiece instead of a concave lens, as Galileo used. This allowed for a wider field of view and greater magnification, however the images were inverted, so anything observed through the telescope was upside down. The issue with this design was that in order to increase magnification further, the telescope had to be longer. The longest of these telescopes noted was 150 feet in focal length and was unable to support its own weight. The image above is a rough schematic for the design of this telescope. Image from Wikimedia and is public domain.