Newtonian telescope

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Related to Newtonian telescopes: Newtonian reflector, Reflector telescope
Ray path in Newtonian telescopeclick for a larger image
Ray path in Newtonian telescope

Newtonian telescope

(new-toh -nee-ăn) The first reflecting telescope to be built, developed in about 1670 by Isaac Newton from the ideas of Zucchi and Gregory: Newton turned his attention to reflecting telescopes because he thought (wrongly) that there was no way in which the chromatic aberration of refracting telescopes could be corrected. The Newtonian has a paraboloid primary mirror and a flat diagonal mirror that reflects the light into an eyepiece mounted on the side of the tube (see illustration). A 45° prism can be used as an alternative to the diagonal mirror. The Newtonian is still the form used by many amateurs, although it is somewhat inconvenient to use in larger form. Newton's original telescope had a mirror only 2.5 cm in diameter and made of speculum metal; it had a focal length of about 15 cm and magnified some 30 times.

Newtonian telescope

[′nü′tō·nē·ən ′tel·ə‚skōp]
(optics)
A reflecting telescope in which the light reflected from a concave mirror is reflected again by a plane mirror making an angle of 45° with the telescope axis, so that it passes through a hole in the side of the telescope containing the eyepiece.