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SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Diagram of Sir Isaac Newton's design for a reflecting telescope. Known also as the Newtonian telescope. It worked by concentrating light by reflection from a parabolic mirror, instead of by refraction through a lens. Newton (1642-1727) first displayed this telescope to King Charles II, based on a design of 1668. It had a focal length of 15 cm and could magnify 30-40 times. Inadequate mirrors meant that the Newtonian reflector was not as refined as contemporary refracting telescopes, until 1722, when James Hadley ground a quality parabolic mirror. This drawing was published in the Philosophical Transactions of the Royal Society in 1672.
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