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He described the design in his 1663 publication ''Optica Promota (The Advance of Optics)''. Early attempts to build a Gregorian telescope failed, and it wasn't until ten years later, aided by the interest of experimental scientist Robert Hooke , that a working instrument was actually constructed. Gregory's design pre-dates the familiar form of reflector which Sir Isaac Newton first designed and made around 1670 . The Gregorian telescope consists of two concave Mirror s; the primary mirror collects the light and brings it to a Focus at the secondary mirror where it is reflected back through a hole in the centre of the primary, and thence out the bottom end of the instrument where it can be viewed with the aid of the Eyepiece . This design of telescope renders an upright image, making it useful for terrestrial observations. The Gregorian design has the advantage over Newton's design, in that it requires a shorter tube for the same Focal Length . The design was largely superseded by the Cassegrain Telescope , and is not commonly in use today, other than for Spotting Scope s. SEE ALSO EXTERNAL LINKS |
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