User:Marshallsumter/Early telescope

The early telescopes as manufactured in the Netherlands are refracting. From the Wikipedia article on the telescope: "The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s (the 17th century), using glass lenses."

Keplerian telescope
From the Wikipedia article Refracting telescope: "The Keplerian Telescope, invented by Johannes Kepler in 1611, is an improvement on Galileo's design. It uses a [plano]convex lens as the eyepiece instead of Galileo's [double] concave one. The advantage of this arrangement is [that] the rays of light emerging from the eyepiece are converging. This allows for a much wider field of view and greater eye relief but the image for the viewer is inverted. Considerably higher magnifications can be reached with this design but to overcome aberrations the simple objective lens needs to have a very high f-ratio".

From the Wikipedia article Refracting telescope: "All refracting telescopes use the same principles. The combination of an objective lens 1 and some type of eyepiece 2 is used to gather more light than the human eye could collect on its own, focus it 5, and present the viewer with a brighter, clearer, and magnified virtual image 6."

Air telescope
From the Wikipedia article refracting telescope: "Johannes Hevelius built [an air telescope] with a 45 m (150 ft) focal length and even longer tubeless "aerial telescopes" were constructed".

From the Wikipedia article Aerial telescope: "An aerial telescope is a type of very-long-focal-length refracting telescope built in the second half of the 17th century that did not use a tube. Instead, the objective was mounted on a pole, tree, tower, building or other structure on a swivel ball-joint. The observer stood on the ground and held the eyepiece, which was connected to the objective by a string or connecting rod. By holding the string tight and maneuvering the eyepiece, the observer could aim the telescope at objects in the sky. The idea for this type of telescope may have originated in the late 17th century with the Dutch mathematician, astronomer and physicist Christiaan Huygens and his brother Constantijn Huygens, Jr.,  though it is not clear that they invented it. "

Tubes
"There are indeed ancient tablets that mention astronomers' lenses supported by a golden tube to enlarge the pupil, and in Nineveh a rock crystal lens was found (Pettinato 1998). Maybe one day a new archaeological excavation will find a Babylonian telescope for the first time."

Early lenses
"Lens-shaped crystals have long been known from Bronze Age contexts". These are "usually recognized as short-focus magnifying lenses." From the Wikipedia article Nimrud lens: "The slightly oval lens [40 x 35 mm] has been roughly ground and has a focal point about 110 millimetres (4.5 in) from the flat side. "