![]() By another way of measuring I found it magnified 35 times. The Eye-glass was Plano-convex, and the diameter of the Sphere to which the convex side was ground was about 1/5 of an Inch, or a little less, and by consequence it magnified between 30 and 40 times. ![]() ![]() "The diameter of the sphere to which the Metal was ground concave was about 25 English Inches, and by consequence the length of the Instrument about six Inches and a quarter. He also made all the tube, mount, and fittings. This unique addition allowed the image to be viewed with minimal obstruction of the objective mirror. 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. He chose a spherical shape for his mirror instead of a parabola to simplify construction: he had satisfied himself that the chromatic, and not the spherical aberration, formed the chief faults of refracting telescopes. He devised means for shaping and grinding the mirror and may have been the first to use a pitch lap to polish the optical surface. To create the primary mirror Newton used a custom composition of metal consisting of six parts copper to two parts tin, an early composition of speculum metal. The telescope he constructed used mirrors as the objective which bypass that problem. He had concluded that the lens of any refracting telescope would suffer from the dispersion of light into colours ( chromatic aberration). Isaac Newton built his reflecting telescope as a proof for his theory that white light is composed of a spectrum of colours. 19th century drawing of Newton's reflector
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