Editing Reflecting telescope (section)

==== {{anchor|Herschelian telescope}}Herschelian ====

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 |header=Light paths
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 |image1=Herschel-Lomonosov reflecting telescope.svg
 |image2=Off-axis optical telescope diagram.svg
 |caption1=Herschelian telescope
 |caption2=Schiefspiegler telescope
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The '''Herschelian''' reflector is named after [[William Herschel]], who used this design to build very large telescopes including the [[40-foot telescope]] in 1789. In the Herschelian reflector the primary mirror is tilted so the observer's head does not block the incoming light. Although this introduces geometrical aberrations, Herschel employed this design to avoid the use of a Newtonian secondary mirror since the [[speculum metal]] mirrors of that time [[tarnish]]ed quickly and could only achieve 60% reflectivity.<ref>[http://catalogue.museogalileo.it/indepth/Telescope.html catalogue.museogalileo.it - Institute and Museum of the History of Science - Florence, Italy, Telescope, glossary]</ref>