Keplerian telescope

This instrument used a pair of fine-pitched screws to move two pointers in the focal plane of a Keplerian telescope.

Johannes Kepler proposed an improvement on the design that used a convex eyepiece, often called the Keplerian Telescope.

The Keplerian Telescope, invented by Johannes Kepler in 1611, is an improvement on Galileo's design.

After the invention of the telescope Kepler set out the theoretical basis on how they worked and described an improved version, known as the Keplerian telescope, using two convex lenses to produce higher magnification.

Additionally, he did fundamental work in the field of optics, invented an improved version of the refracting telescope (the Keplerian Telescope), and mentioned the telescopic discoveries of his contemporary Galileo Galilei.

Besides combining a Keplerian telescope with a camera, there are also dedicated secondary lens afocal attachments that mount on the front of a camera lens to work in the role of a teleconverter, technically called teleside converters.

In 1641 he built an observatory on the roofs of his three connected houses, equipping it with splendid instruments, including ultimately a large Keplerian telescope of 45 m (150 ft) focal length, with a wood and wire tube he constructed himself.

The next big step in the development of refractors was the advent of the Achromatic lens in the early 18th century that corrected chromatic aberration seen in Keplerian telescopes up to that time, allowing for much shorter instruments with much larger objectives.

In Oculus Enoch et Eliae, besides describing one of his inventions, an eyepiece for a Keplerian telescope, which left the image reverted, it also contained a long section on binocular telescopes, which greatly influenced other telescope-makers and opticians in the next century.

In 1611, Johannes Kepler described how a telescope could be made with a convex objective lens and a convex eyepiece lens and by 1655 astronomers such as Christiaan Huygens were building powerful but unwieldy Keplerian telescopes with compound eyepieces.