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Gregorian Reflecting Telescope


Date Late 1700s
Dimensions English Metric
Main Tube Length 5.2in 131mm
Main Tube Diameter 1.2in 31mm
Total Length 7.1in 180mm
Primary Mirror Diameter 1.0in 25mm


This telescope has a very small brass cylindrical barrel.  The primary mirror is a concave paraboloid, with a central hole, and is kept in place at the rear of the barrel with a screw-in backing plate.  The small secondary mirror is a concave ellipsoid.  It is attached by a slender arm to a screw-driven carrier which slides along the front interior part of the barrel.  This configuration of primary and secondary mirrors is called Gregorian.  Both mirrors are speculum.  The focusing thumbscrew, at the eyepiece end of the barrel, attaches to the secondary mirror carrier through a slot near the eyepiece end of the barrel. The eyepiece tube screws into a hole in the center of the backing plate, which holds the primary mirror in place.  The two-lens eyepiece is the Huygens type.  The telescope is not signed by the maker.  This telescope is certainly among the smallest ever produced.




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