<P> In 1666 Isaac Newton , based on his theories of refraction and color , perceived that the faults of the refracting telescope were due more to a lens 's varying refraction of light of different colors than to a lens 's imperfect shape . He concluded that light could not be refracted through a lens without causing chromatic aberrations , although he incorrectly concluded from some rough experiments that all refracting substances would diverge the prismatic colors in a constant proportion to their mean refraction . From these experiments Newton concluded that no improvement could be made in the refracting telescope . Newton 's experiments with mirrors showed that they did not suffer from the chromatic errors of lenses , for all colors of light the angle of incidence reflected in a mirror was equal to the angle of reflection , so as a proof to his theories Newton set out to build a reflecting telescope . Newton completed his first telescope in 1668 and it is the earliest known functional reflecting telescope . After much experiment , he chose an alloy ( speculum metal ) of tin and copper as the most suitable material for his objective mirror . He later devised means for grinding and polishing them , but chose a spherical shape for his mirror instead of a parabola to simplify construction . He added to his reflector what is the hallmark of the design of a `` Newtonian telescope '' , a secondary `` diagonal '' mirror near the primary mirror 's focus to reflect the image at 90 ° angle to an eyepiece mounted on the side of the telescope . This unique addition allowed the image to be viewed with minimal obstruction of the objective mirror . He also made all the tube , mount , and fittings . Newton 's first compact reflecting telescope had a mirror diameter of 1.3 inches and a focal ratio of f / 5 . With it he found that he could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus . Encouraged by this success , he made a second telescope with a magnifying power of 38x which he presented to the Royal Society of London in December 1672 . This type of telescope is still called a Newtonian telescope . </P>
<P> In 1666 Isaac Newton , based on his theories of refraction and color , perceived that the faults of the refracting telescope were due more to a lens 's varying refraction of light of different colors than to a lens 's imperfect shape . He concluded that light could not be refracted through a lens without causing chromatic aberrations , although he incorrectly concluded from some rough experiments that all refracting substances would diverge the prismatic colors in a constant proportion to their mean refraction . From these experiments Newton concluded that no improvement could be made in the refracting telescope . Newton 's experiments with mirrors showed that they did not suffer from the chromatic errors of lenses , for all colors of light the angle of incidence reflected in a mirror was equal to the angle of reflection , so as a proof to his theories Newton set out to build a reflecting telescope . Newton completed his first telescope in 1668 and it is the earliest known functional reflecting telescope . After much experiment , he chose an alloy ( speculum metal ) of tin and copper as the most suitable material for his objective mirror . He later devised means for grinding and polishing them , but chose a spherical shape for his mirror instead of a parabola to simplify construction . He added to his reflector what is the hallmark of the design of a `` Newtonian telescope '' , a secondary `` diagonal '' mirror near the primary mirror 's focus to reflect the image at 90 ° angle to an eyepiece mounted on the side of the telescope . This unique addition allowed the image to be viewed with minimal obstruction of the objective mirror . He also made all the tube , mount , and fittings . Newton 's first compact reflecting telescope had a mirror diameter of 1.3 inches and a focal ratio of f / 5 . With it he found that he could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus . Encouraged by this success , he made a second telescope with a magnifying power of 38x which he presented to the Royal Society of London in December 1672 . This type of telescope is still called a Newtonian telescope . </P>
who built the first practical telescope and developed a theory of colour
who built the first practical telescope and developed a theory of colour
Isaac Newton
Isaac Newton